Gro-Tsen's 2025– Twitter archive

Tweets by year: 2018, 2019, 2020, 2021, 2022, 2023, 2024, 2025–.

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@Ag2Adam It is the same English name “Indian Oil” transliterated in Tamil script instead of Devanagari.
I think putting “1982” on the United Kingdom because of the Falklands War is a bit of a stretch.␤␤(Also, I think the meaningful date is not “when last invasion started” but “when last invasion stopped”, so Ireland definitely shouldn't be 1649. 😅) x.com/amazingmap/sta…
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And if the point was to not just address the Hindi-speakers in India, then this fails too, because Devanāgarī isn't widely used outside of Hindi.␤␤Or does the Indian Oil logo read “இந்தியன் ஆயில்” (this is still English!) in Tamil Nadu? 🤔
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I don't know Hindi, but I'm pretty sure the way you'd say “Indian oil” in Hindi (maybe “भारतीय तेल” or sth of the sort) isn't to transliterate the English “English oil” into the script. I know for a fact that Hindi has a native word for “India” (one of the few words I know). 😁
I was glancing through a BBC news article photo when it struck me that the logo of the India company Indian Oil says “इंडियन ऑयल”, which is the transliteration in Devanāgarī script of “Indian Oil”. Transliteration, not translation! This is English, but written in Devanāgarī. 😮 pic.x.com/XAfR0mzMWW
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en.wikipedia.org/wiki/Fuck
The meticulously detailed and beautifully illustrated Wikipedia page for the profanity “fuck” and its wide gamut of meanings is a wonderful example of how Wikipedia can turn a seemingly frivolous subject into something simultaneously wonderful and absofuckinglutely hilarious.
RT @ThatEricAlper: pic.x.com/exHsxR5lBf
Un billet de blog sur les Prunus en fleurs, où et comment en voir en Île-de-France: madore.org/~david/weblog/…␤␤(Billet publié hier, mais je viens d'ajouter des photos dessus, donc j'annonce maintenant.)
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See? I'm beginning to warm up to the “everybody is twelve” theory of American reality. sg.news.yahoo.com/viral-everyone…
Of course darling you can be Braveheart and Maverick from Top Gun and Master Chief from Halo and Superman and whatever you want. You're twelve, so of course you want to impress us all. x.com/WhiteHouse/sta…
RT @CR1337: pic.x.com/ta3fefygJl
Current mood: x.com/SaarelaHC/stat…
RT @T3chFalcon: Works everytime pic.x.com/Ybm5Qyq9rK
This looks like it could actually be a fun game to play. x.com/TheFigen_/stat…
RT @brontyman: pic.x.com/c2FKEyYakc
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Pour les Franciliens: ça vaut vraiment la peine de faire un tour à Chèvreloup pour voir les Prunus en fleurs. Ces arbres-ci (à gauche en entrant, à part des autres) sont parmi les plus précoces, mais au fil des semaines il y a plein d'autres fleurs magnifiques qui vont sortir.
Enfin! Ça aura pris cinq ans, mais aujourd'hui j'ai fini par réussir à revoir ces Prunus cerasifera v. divaricata aussi beaux qu'en 2021. 😍 pic.x.com/FF9SkCifAw x.com/gro_tsen/statu…
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Anyway, if I were to write a constitution, I would make sure to explicitly give the legislature, and not the president, the power to declare War (and maybe also to “grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water”). Just to be sure.
RT @nono2357: Vérifier l'âge des internautes ? La mesure est inefficace, dangereuse, et précipitée, selon 370 universitaires spécialisés da…
RT @amazingmap: Vehicle registration plate formats across Europe pic.x.com/6r5iLOOkA0
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Full comment (by Spencer A. McDaniel) here: reddit.com/r/AskHistorian…
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The earliest depictions of dragons with legs and wings still show them with long, snake-like bodies. […] It was only really in the twentieth and twenty-first centuries that people began to imagine dragons that substantially resemble prehistoric reptiles.”
#TIL on Reddit /r/AskHistorians: “Throughout ancient and medieval European art and literature, dragons are consistently depicted as essentially giant snakes. […] Europeans only began to depict dragons with legs and wings in the second half of the thirteenth century. […]
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… so even with a 2 day margin of error, there can be no doubt that Easter is the next Sunday, hence 2026-04-05.␤␤(Admittedly, I did check before posting, but I would have been really surprised if I had been wrong on that one.)
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… it still follows the true moon fairly well. So if 2026-03-02 is a full moon ±1 day, the next full moon is on 2026-03-31 (29 days later), maybe ±2 days. Since March 21 is safely between the two, this has to be the Paschal moon. Now 29≡1 mod 7, so 2026-03-31 is a Tuesday, …
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The general definition of Easter is “the Sunday strictly following the first ecclesiastical full moon that occurs on or after March 21”. The actual computus rules for ecclesiastical moon are complicated (see my old page madore.org/~david/misc/ca… if you want details), but …
The date of (Gregorian) Easter is generally annoying to compute, but sometimes you can do it easily.␤␤Tonight (2026-03-02, this being a Monday), I noticed the moon was about full. So I knew that Easter had to fall on 2026-04-08. Why? ⤵️
Technology is in decline. The quality of cameras has considerably decreased in the last ~20 years. They no longer accurately reflect the sexy handsome young man I am. The same even hold for mirrors.
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@Grogro18985296 Oui, tout à fait.
On poste souvent des bouts de copies d'élèves pour se moquer des erreurs ou de la mauvaise orthographe ou écriture (perso je ne fais pas ça).␤␤Mais là, la personne qui a écrit ça a dû être calligraphe dans une vie antérieure. 🤩 pic.x.com/LEEmY2DvRG
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But more importantly, the above counterarguments are SUPER STANDARD. If you haven't heard them you shouldn't be discussing nuclear weapons or geopolitics. If you have, then you should at least be addressing them (for they are not infallible either, of course). •9/9
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And pointing to someone who took the gamble, failed, and got killed precisely because he took that gamble, is not the perfect argument you think it is to prove “now everyone is going to try the gamble because this shows the importance of succeeding”. 🤦 •8/9
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… but you can't predict whether it will be >0 or <0 by a super general jejune argument that basically consists of ignoring risks and shrieking “high reward!!!”. You need to look at specific circumstances.␤␤All winners of the lottery got rich. Doesn't mean you should play.␤␤•7/9
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Like most actions in geopolitics, “trying to build nuclear weapons” is a matter of balancing risks and rewards. The balance is generally around 0 by basic game theory (otherwise everyone would do it — or nobody would do it). In individual cases it's a bit above or below, … •6/9
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… or indirectly by putting sanctions upon you which make your economy worse and increase your chances of being overthrown (also witness Iran!).␤␤So the gamble has gains if you succeed, but it also has associated risks. Ignoring the latter is dishonest.␤␤•5/9
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Second, everyone also understands that “building nukes” is a gamble. If you succeed, then, yes, you get some protection. But, as long as you don't succeed, trying puts you at risk, because other countries try to stop you from succeeding. Either directly (witness Iran), … •4/9
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… Their advisors also know this. And having one more example to add to the list won't change anything.␤␤Did we witness any new countries start an attempt to construct nuclear weapons after the fall of Qaḏḏāfī? If so, this is what you should point to.␤␤•3/9
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First, “having nuclear weapons offers protection against foreign intervention” is not new information in any way. Anyone who knows anything about geopolitics has known this for at least 60 years. Leaders who might choose to pursue nukes know this. … •2/9
I'm seeing a lot of bad “Khamenei was killed because he didn't have nuclear weapons yet, so the Iranian example will push more rogue régimes to develop nuclear weapons ASAP so they don't get overthrown” bad takes.␤␤So let me repeat the (standard!) counterargument: …␤␤•1/9
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(The truth is probably that they also killed #2 and #3 in some plausible line of succession, not people they themselves picked to replace #1, but I'm not sure Trump understands the difference, and if someone has a strategy in this mess it's definitely not he.)
“We accidentally killed all the puppets we were planning to put in place to replace the leader we killed” has to be a line out of ‘The Onion’. x.com/jonkarl/status…
RT @DoctorPerin: All those “my therapist told me something” tweets pic.x.com/9bnwTqNUxz
RT @gro_tsen: I wonder what became of the person who made this interesting analysis. 🤔 pic.x.com/Cch6ReE1Ex x.com/TulsiGabbard/s…
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@Valriepierre10 Bien sûr: il n'y a qu'en France que ce système existe. (Même si certains pays, comme les USA, ont qqch d'un peu analogue dans la sélection à l'entrée des universités.)
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@JacqBens … ce qui ne marche correctement que si on parle de preuves en logique intuitionniste (ou alors il faut ajouter la fonction “call/cc” côté informatique, qui ouvre son propre sac de nœuds).␤␤PS: Les transparents de mon cours sont là: perso.enst.fr/madore/inf110/…
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@JacqBens Mais au contraire! J'enseigne notamment un cours intitulé «logique et fondements de l'informatique» dont une partie importante est d'expliquer la correspondance de Curry-Howard entre typage en informatique et preuves en mathématiques … pic.x.com/SMlvtqpBQl
Une réflexion à 0.02¤ sur mon blog sur la neurologie des mathématiques, et le rapport entre maths et endormissement: madore.org/~david/weblog/…
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@Sainte_Aytique Moui, même s'il est sur X (ou sur Bluesky, où j'ai posté la même chose), la probabilité qu'il tombe sur mon message et se reconnaisse me semble bien faible, quand même.
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Alerte! Des Prunus cerasifera en fleurs eux aussi. Il va être temps pour moi de faire un tour à Chèvreloup. x.com/gro_tsen/statu… pic.x.com/eSwFuKgQy5
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… qu'une table de jeunes pas loin de là était tout d'un coup devenue bizarrement silencieuse et l'un de nous a chuchoté «en fait je crois qu'ils parlaient de maths de prépa tout à l'heure». 😅
Je dirais «il faut se méfier de qui peut entendre ce qu'on raconte au restaurant», mais je me souviens d'un repas au “chinois canonique” entre examinateurs des ENS où on a commencé à dire des trucs pas très publics avant de se taire assez vite en se rendant compte … x.com/gro_tsen/statu…
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Bon ils sont partis avant que je me décide à dire qqch. Mais je ne sais pas si j'avais vraiment qqch d'intelligent à dire, et je ne voulais surtout pas faire «j'ai tout écouté, et au fait je connais votre prof et j'enseigne à Télécom; et sinon, vous bossez trop, jeune homme».
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Ah ben maintenant il est en train de dire que son classement des grandes écoles c'est X, Ulm, Centrale, Mines, Ponts, ENS Paris-Saclay, ENSTA, ENSAE, et Télécom tout en dernier, et qu'il ne sera pas du tout content s'il a Télécom.␤␤Sale gosse!
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Bon, mais de façon plus problématique, cet élève bosse manifestement trop. Et est à la limite de craquer. Et son père est limite en train de l'engueuler en lui parlant de sacrifices que ses grands-parents ont fait. J'hésite un peu à dire quelque chose.
Je suis au restaurant et la table à côté il y a, en train de manger avec son père, un élève de classe prépa scientifique qui se plaint de son prof de maths. Prof que je connais très bien (j'étais agrégé-préparateur à l'ENS en même temps que lui). 😆
RT @Teh_Snowflake: @MorePerfectUS @verge pic.x.com/nTZ2L9PysN
Cette année les magnolias sont TRÈS en avance! pic.x.com/c6nCiUkIb0 x.com/gro_tsen/statu…
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[Tweet id: 255784560904773633 / archive.is/P4gNm ] pic.x.com/lfttbZsQCC
Well, it's almost as though that meaningless FIFA Peace Prize didn't mean anything. 😑 bbc.com/news/live/cn5g…
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@alfosn The BBC writes about “the strange British phenomenon of the snatched backseat picture”: bbc.com/news/articles/…
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“Our startup has developed a startling new product: the Big Realistic Artificial Intelligence Network consists of about 90 billion living cells, matured over a period of dozens of years, capable of reproducing even more amazing feats than other AI models…” 😬
Also, I am curious to know what happens when the promising new fields of “let's perform computations using human brain cells” and artificial intelligence meet. 🤔 x.com/gro_tsen/statu…
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I don't know if, a week later, brain-in-a-vat started philosophizing about who built the walls and who created the guns and what the meaning of life and death are, but, holy sh😓t, the simulation argument just got a whole lot stronger!
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THE MOVIE ‘MATRIX’ WAS NOT SUPPOSED TO BE AN INSTRUCTION MANUAL, GUYS! 🤬
OK, let me get that straight: we took some actual living human brain cells — aka, a brain-in-vat — and went all Descartes Demon on them by making them experience the simulated world of the game ‘Doom’ for ❝research❞ purposes? 😱 newscientist.com/article/251738…
RT @Pirat_Nation: Myrient, a major video game preservation archive hosting over 390 terabytes of organized ROMs, ISOs, and collections, is…
The only person who always got his work done by Friday was Robinson Crusoe.
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Update: I solved it (yes, E is computably enumerable, and the proof uses a variant of Rosser's trick). x.com/gro_tsen/statu…
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This trick answers the following question that I was puzzling about (the answer is, yes, E is computably enumerable; and I sketch a proof in my question): x.com/gro_tsen/statu…
I asked a question on MathOverflow about a version of “Rosser's trick” in the context of computability (I give an example and ask in what other places this trick is used): mathoverflow.net/q/508591/17064
C'est le printemps! 🌸🥰 pic.x.com/04YiOWYEML
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@bortzmeyer @espie_openbsd Je pose ça là: x.com/i/status/20260…
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@Ag2Adam Yes, that's what I had guessed as well. But because of this “politeness”, now nobody outside of the experts know what the actual problem is. (Like: is it complete nonsense? or is there a clear identifiable error somewhere?)
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… since the sun (and shadows cast by the sun) turn “counterclockwise” in the southern hemisphere, one might argue that it makes sense to use opposite-direction clocks there.␤␤(I'm not being 100% serious here, but I still do wonder.)
I wonder if southern hemisphere countries considered using clocks whose hands turn in the opposite direction from standard (let's call them European) clocks.␤␤I mean, I presume the “clockwise” orientation was chosen to imitate the way the shadow cast by a sundial turns: …
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Specific example: Heisuke Hironaka announced in 2017 a proof people.math.harvard.edu/%7Ehironaka/pR… of resolution of algebraic singularities in all characteristics (he is a renowned expert and had done the characteristic 0 case 50+ years before). What do experts think about it? 🤷
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For example, when a serious mathematician announces the proof of a major result and that proof is never published, I guess we are to assume that there is something wrong with it. But how deeply wrong? Where are the errors? Is something salvageable? There is no way to know! 😕
One of the extremely annoying things about the current preprint+publication system in math is that there is no way of staying informed about errors in preprints and published papers.␤␤“Experts know”, but this knowledge isn't passed on publicly. 😠
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(And note that s(m) is allowed to be defined even if {n∈E : p(n)=m} = ∅. Otherwise we could get the conclusion that E is computably enumerable by taking for p the identity.)
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Again, does this imply E is c.e.?␤␤To be perfectly clear, the condition is:␤␤‣ ∀ total computable p:ℕ→ℕ ∃ s:ℕ⇢ℕ partial computable ∀m∈ℕ ((∃n∈E (p(n)=m)) ⇒ s(m)↓ ∧ s(m)∈E ∧ p(s(m))=m)
Maybe this condition on E⊆ℕ (implied by the quoted one, perhaps equivalent) is more manageable:␤␤‣ For every total computable p:ℕ→ℕ there exists s:ℕ⇢ℕ partial computable s.t. for all m∈ℕ, if {n∈E : p(n)=m} has at least one element, then s(m)↓ is one of them. x.com/gro_tsen/statu…
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Even more informally, “if I can computably perform any computation that can be performed from an enumeration of E, can I computably enumerate E?”. 🤔␤␤(I can enumerate an infinite subset of E, at least.)
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In other words, the condition requires that there is a computable way (h) to transform an oracle program e taking as oracle any enumeration γ of E, and which always terminates for such an oracle, into a value φ_e^γ(0) computed by such a program.
Trying to unwrap what the following condition on E⊆ℕ means in practice:␤␤‣ There is h:ℕ⇢ℕ partial computable s.t. if e∈ℕ satisfies φ_e^γ(0)↓ for all γ:ℕ→ℕ with image E, then h(e)↓ is one among the φ_e^γ(0).␤␤Does this imply E is computably enumerable? (Maybe stupid!)
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@BhTyphon Par ailleurs, «où on peut aller en bateau» c'est essentiellement ce qui s'appelle un bassin versant, il y a une carte très bien pour ça sur Wikipédia, et oui, ça va souvent très loin: commons.wikimedia.org/wiki/File:Ocea… pic.x.com/AkzgwajV9F
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🗯️ «L'AMBROISIE NE SE MANGE PAS, ELLE SE BOIT!» pic.x.com/Dvr5a7tubi
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«Les jeunes, de nos jours, ils ne savent plus se tenir à table, ils mangent leur ambroisie au lieu de la boire! L'AMBROISIE NE SE MANGE PAS, ELLE SE BOIT!» fr.wikipedia.org/w/index.php?ti… pic.x.com/Dt2cZTXaBp
J.-B. Boomer sur Wikipédia: «Aujourd'hui tout le monde déforme les connaissances anciennes en les mettant à leur sauce. D'ailleurs il n'y a qu'à considérer le langage totalement déformé et vulgaire des jeunes de maintenant qui croient en savoir plus que les anciens.» 🤣 pic.x.com/DGd47ANpTR
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@fgrosshans Oui, ça c'est ce que je m'attendais à voir. C'est pour ça que j'ai été surpris de voir que le rouge avait plutôt bien tenu (chez les V5/V7/VSign) et le violet nettement moins.
RT @dmayhem93: pic.x.com/OWxr1oOsbM x.com/AnthropicAI/st…
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… He doesn't even speak French, by the way. I wonder what he does with his days. Play golf and go to the beach on the French riviera?
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… Anyway, the 🇺🇸 ambassador to 🇫🇷 just refused to do this only job. But here it's clear that the post serves only one purpose, which is to provide with the president's daughter's father-in-law (also a convicted felon) with a pleasant sinecure at the US taxpayers' expense. …
I have to say, in 2026, I'm not sure what the point of having ambassadors (as opposed to embassies) still is, when heads of state/gvt can call each other directly: basically the only job the ambassador of X to Y has is to receive a scowl when X does something Y doesn't like. … x.com/FRANCE24/statu…
Pas surpris que les VPen effaçables aient mal tenu à la lumière (je suis même plutôt étonné que le bleu ait si bien résisté), en revanche je suis nettement plus surpris par la différence entre les V5 rose et violet d'une part et les V5 rouge et bleu de l'autre. x.com/gro_tsen/statu…
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Les deux scans à 4 mois d'écart, alignés aussi précisément que j'ai pu: je dirais que les encres qui ont le plus souffert sont les V5 rose et violet, et les VPen¹ de toutes les couleurs sauf le bleu.␤␤1. Normal: ils sont effaçables. pic.x.com/WJTT84Yy71
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La même page (scannée avec les mêmes réglages), après avoir laissé la feuille derrière une fenêtre exposée au jour (mais rarement au soleil direct) pendant 4 mois. La partie inférieure vient d'être écrite, pour comparer: pic.x.com/W4gN1wGEv1
Un petit billet de blog sur mon ressenti de l'étendue de l'espace (pour faire pendant à celui que j'avais écrit il y a un an sur le passage du temps): madore.org/~david/weblog/…
This is how I imagine YouTube Shorts was born:␤␤wumo.com/wumo/2026/02/22 [Wumo comic for 2026-02-22] pic.x.com/pRuLpJDSLf
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I watched this video 🔽 last year, but I think it's worth adding to the above list, because it's really good. It's about trying to explain why it's so hard to explain how math is useful, yet why this doesn't imply that math is useless. x.com/gro_tsen/statu…
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👉 We desperately need laws that exempt Web archiving services from any kind of liability (whether under copyright, slander, or any other kind), as long as they don't edit the pages they archive, and democratic governments to actually set up some more, and fund them.
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Sadly, the only other available Web archiving service, the venerable (and reputable) Internet Archive, are crumbling under the load, and under financial and legal difficulties.␤␤Also, they seem to have broken HTTP archiving, so my own site can no longer be archived there. 😭
Good to know: Archive dot is (which exists under various other domains), whose operator and motives are shrouded in mystery, has been found editing archived snapshots, so should not be considered reliable: boingboing.net/2026/02/21/arc…
RT @alfosn: Deeply fascinated by this distinctively British genre of photography pic.x.com/CbKoPZYrUy
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theguardian.com/us-news/2026/f…
Just to remind anyone who isn't a US citizen that travel to that country is not safe and you have no protection against arbitrary detention, even if you check all “safe” boxes as a white elderly middle-class British woman with a valid visa and no criminal record named “Karen”:
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So I guess now Trump is going to declare a 150% tariff on the Supreme Court or something. x.com/atrupar/status…
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😬 x.com/atrupar/status…
I really don't envy the poor staffers who had to explain the ruling to a guy who is clearly reaching the limits of his cognitive abilities. x.com/atrupar/status…
The 💩 has hit the 🪭. x.com/i/status/20248…
RT @Reuters: BREAKING: Supreme Court rules against Trump's tariffs enacted under a federal law meant for national emergencies https://t.co/…
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@roystgnr More research needed! BRB asking for a grant.
RT @jmduke: One of the funnier GDPR disclosures I've seen in a while. pic.x.com/tSsZwaGTYb
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… And another giant-ass ocean covering just under one hemisphere? I'm sorry, but all of this is very sloppy world-building.
If you were to show me a map of the Earth and tell me it's a fantasy world you're creating, I'd say it's far too neat to be plausible. One giant uninhabited continent centered almost right at the South Pole? The North Pole similarly right in a neat little ocean? …
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(The higher you go in dimension, the more kiki the 1-norm and ∞-norm become, whereas the 2-norm remains unquestionably bouba.)
Since I often say that we shouldn't name mathematical concepts (or anything, really) after people, I now propose to rename “Hilbert spaces” to “bouba spaces” and “Banach spaces” to “kiki spaces”, because everyone will instinctively know L² is bouba and L¹ is kiki. 😁 x.com/gro_tsen/statu…
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Wikipedia for those who don't know what the “bouba/kiki effect” is: en.wikipedia.org/wiki/Bouba/kik…
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Link to the ‘Science’ paper: science.org/doi/10.1126/sc…
The bouba/kiki effect is mind-blowing to start with, but to discover that it even works on… baby chickens?… is doubly mind-blowing.␤␤(Think more of a bouba kind of explosion than a kiki one.)
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A series of videos on the Guianas (their history, geography and demographics, and how they ended up being so different from the rest of South America). youtube.com/watch?v=iaR53L…
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On the interaction between Britain's Caribbean colonies and the American Revolution (why these colonies didn't join the revolution, but what part they eventually played in it anyway, and conversely how the revolution impacted them). youtube.com/watch?v=DIPdSY…
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L'histoire de la cartographie en France, la création et la raison d'être de l'IGN (racontée avec un certain humour). youtube.com/watch?v=rt2yuR…
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A history of the linguistic divide of Belgium from the Roman empire to the present day. youtube.com/watch?v=GR8HgP…
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I have an immense respect for people who actually write Wikipedia articles. On the other hand, I have nothing but contempt for those who care not about the content but about the process and spend their days just performing bureaucracy and policing others. en.wikipedia.org/w/index.php?ti…
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en.wikipedia.org/w/index.php?ti…
This is exactly the sort of rule-obsessed punctilious bureaucratic gatekeeping that drives people away from contributing to Wikipedia: on the one hand they tell you “anyone can edit”, on the other, your edits immediately get reverted for violating rule 42(F)(u)¶c-k.
RT @tomshardware: In a blind test, audiophiles couldn't tell the difference between audio signals sent through copper wire, a banana, or we…
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@Jilcaesel @laurentbercot Ok. Let me amend:␤␤I think she's actively looking for ways for people to remember she ever existed in some other way than “the Prime Minister who lost to a salad”. (So even sucking up to Donald Trump is less humiliating.)
RT @PetitPiedDessin: pic.x.com/40Uw6rv0EW
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@laurentbercot I think she's actively looking for ways for people to remember she ever existed.
I suspect she loves Donald Trump so much because Donald Trump really hates salads. 😁␤␤[Tweet id: 2023061720017822019] pic.x.com/hucfiX1aPN
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@JDHamkins I had to leave a little clue for my careful readers to realize the screenshots were fake because they were otherwise so perfectly believable and realistic.
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@antoineducros @pianocktailiste @canard_milliard Oui, il y a deux questions différentes qui sont confondues dans la question, mais la réponse aux deux est évoquée.
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@canard_milliard @Jojo_le_poisson (Le but principal étant évidemment surtout d'empêcher les bloqueurs de pub.)
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@canard_milliard @Jojo_le_poisson Quelque chose comme du HTML signé et chiffré que tu ne peux ni inspecter ni modifier. Les détails n'ont jamais été super clairs, et même ceux qui l'étaient ne l'étaient pas pour moi, mais l'idée était en tout cas dans cette direction.
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@canard_milliard @Jojo_le_poisson C'est plus ou moins ce qu'essayait de faire l'initiative «Web Integrity» de Google, mais heureusement pour notre liberté à tous il semble qu'ils aient (provisoirement?) renoncé.
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@Jojo_le_poisson L'inspecteur est surtout super utile pour faire disparaître facilement un élément qui nous emmerde. (Click droit et «delete note», ou bien ajouter «display: none» comme propriété CSS de l'élément.)
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@pianocktailiste @antoineducros @canard_milliard En clair, le problème est que l'orbite circulaire est possible pour une force en ∝ r^e (ici e = 1−n), mais elle est instable pour e ≤ −3 si j'en crois physics.stackexchange.com/q/263611/39931 — ceci étant, je ne sais pas en quoi elle se transforme si on la perturbe un peu.
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@Jojo_le_poisson … Il y a juste un petit peu de connaissance du HTML et de pratique nécessaire pour identifier l'élément qu'on veut modifier et comment (notamment pour changer une image), et c'est plus ou moins facile selon le site, mais c'est rarement vraiment dur.
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@Jojo_le_poisson Directement dans le navigateur. Sous Firefox j'ouvre l'«inspecteur» (clic droit → “Inspect”) et je modifie le texte des éléments que je veux de l'arbre de la page Web. Les polices restent ce qu'elles étaient. …
Just a friendly reminder that a “screenshot” not accompanied by a link allowing you to check the screenshot is absolutely trivial to fake. pic.x.com/D1jVBwCFDv
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@canard_milliard @pianocktailiste @antoineducros C'est pas un s.e.v. de dimension n−2 non plus, c'est un élément du carré extérieur en.wikipedia.org/wiki/Exterior_… de l'espace vectoriel des vecteurs, euh, “usuels”. (Pour un mathématicien, ça reste des vecteurs, juste pas les mêmes. Mais les champs magnétiques peuvent bien s'ajouter.)
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(For victimhood, it's a bit more debatable, because victimhood is about something done TO you, not done BY you, it's about consequences and not causes. And things done to your parents do have an impact on you, so victimhood can be inherited to an extent, unlike glory or shame.)
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The same goes for shame, by the way.␤␤IMO the only things that should give you pride or guilt are things that you did or caused to be done.␤␤Certainly nothing that happened before your birth should give you either of these feelings (you are not their cause but their consequence).
I really have a hard time wrapping my mind around the concept of chauvinism.␤␤Being proud of one's country seems to me as incomprehensible as being proud of the room one is standing in because previous people standing in the same room did great things.
Interesting answer to a question on Reddit's /r/AskHistorians gives some important context to the simplistic portraying of Semmelweis as a misunderstood genius who couldn't get the simple point “just wash your hands!” across to his day's bigoted doctors: reddit.com/r/AskHistorian…
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@Ced_haurus The Internet of Things: x.com/gro_tsen/statu…
RT @Ced_haurus: Alors celle là, elle est pas mal…␤Le mec voulait s’amuser a contrôler son robot aspirateur DJI avec une manette de PS5, 670… x.com/frandroid/stat…
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@pianocktailiste @canard_milliard @antoineducros Ben tu peux au moins imaginer la situation en dimension n=2 (c'est la situation n=3 quand il y a invariance par translation selon un axe). Le champ magnétique (ou la notion de vitesse de rotation) a alors une seule composante: on voit bien que ce n'est pas un vecteur.
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@pianocktailiste @canard_milliard Peut-être que je devrais dire les choses autrement, en fait: le produit vectoriel de dimension 7, il n'est pas invariant sous les rotations de l'espace (seulement sous certaines d'entre elles, justement ce groupe G₂). Alors que les lois du magnétisme, on veut penser que si.
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@dodecahedra For those: who want to know more about the theory behind this, see the paper by B. Grünbaum, “The Construction of Venn Diagrams” (College Math. J. 15 (1984) 238–247, jstor.org/stable/2686332 (and yes, one can continue for larger values of n). x.com/gro_tsen/statu…
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@laurentbercot Merci, je vais regarder ça avec un intérêt strictement scientifique et documentaire.
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@canard_milliard @pianocktailiste … (Enfin, à moins de vouloir développer une théorie physique farfelue dans laquelle l'espace de dimension 7 aurait non pas juste une structure euclidienne mais une structure octonionique — enfin, une “structure sous G₂” en.wikipedia.org/wiki/G2_(mathe… mais je ne détaille pas.)
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@canard_milliard @pianocktailiste … Et le fait qu'il y ait en dimension 7 une sorte de produit vectoriel, lié aux octonions, n'a vraiment aucun rapport avec le schmilblick. Celui-ci va juste modéliser certaines rotations très particulières (elles-mêmes liées aux octonions). Il faut oublier ce truc. …
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@canard_milliard @pianocktailiste … La représentation des rotations par un vecteur donnant l'axe et la vitesse de rotation est spécifique à la dimension 3. En général, une rotation ça se représente par une matrice antisymétrique (algèbre de Lie tangente à SO_n, en fait). …
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@canard_milliard @pianocktailiste D'ailleurs, on peut aussi argumenter comme ceci: un champ magnétique constant provoque sur les particules chargées l'effet d'une rotation uniforme. Or en dimension n il y a n·(n−1)/2 dimensions de rotation. Ça c'est purement géométrique. …
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@canard_milliard @pianocktailiste … C'est vraiment juste l'idée de représenter le champ magnétique par un vecteur qui est spécifique à la dimension 3, et comme je l'ai signalé, ça ne marche pas vraiment bien même en dimension 3 à cause de ce qui se passe dans un miroir. x.com/gro_tsen/statu…
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@canard_milliard @pianocktailiste … marche sans aucun problème particulier en n'importe quelle dimension, et qu'elle se conforme à ce que je viens de dire, et donne n·(n−1)/2 dimensions de «champ magnétique» (et n de «champ électrique»). …
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@canard_milliard @pianocktailiste … Après, évidemment, on peut dire que l'espace ayant dimension 3, se demander ce qui se passerait en une autre dimension relève de la branlette intellectuelle, mais il se trouve que la formulation relativiste des lois de Maxwell …
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@canard_milliard @pianocktailiste … et perpendiculairement à elle ce qui signifie que le champ magnétique ne travaille pas. Tout ça est testable expérimentalement et ne fait pas référence à la dimension de l'espace. …
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@canard_milliard @pianocktailiste Parce que ce sont les propriétés physiquement observables du champ magnétique avant de se demander par quel objet mathématique on va le décrire: ça agit sur les particules chargées, proportionnellement à leur charge, linéairement en leur vitesse, …
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(And no, I have no idea what this means, so don't ask me.)
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(I'm taking a dark energy density of 5.8×10⁻³⁰ g/cm³ from pdg.lbl.gov/2025/reviews/r… and multiplying by c² to convert to an energy density, i.e., a pressure. Well, actually the pressure sign should be negative for a positive-energy-density cosmological constant.)
USELESS ASTRONOMICAL FACT OF THE DAY:␤␤The pressure associated to dark energy in the universe (in other words, c² times density of dark energy) has a value of approximately 5×10⁻¹⁵ bar (0.5 nPa), which is pretty close to the atmospheric pressure at the surface of the moon.
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@pianocktailiste Je ne «prends» pas les éléments extradiagonaux: B est naturellement une matrice antisymétrique (la matrice qui, appliquée à q·v, donne la force F qui s'exerce dessus, et qui est antisymétrique parce que F⟂v), donc elle a n·(n−1)/2 composantes indépendantes.
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@pianocktailiste … et de toute façon en dimension 7 le champ magnétique doit avoir 21 composantes indépendantes, pas juste 7.
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@pianocktailiste … En tout cas, ce qui est sûr, c'est que l'existence d'un «produit vectoriel» en dimension 7 n'a aucun rapport avec le champ magnétique. Le champ magnétique fait sens en toute dimension, le produit vectoriel dont on parle seulement en dimensions 1, 3 et 7; …
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@pianocktailiste … Ou encore on peut mettre E et B ensemble en relativité et voir ça comme un truc de dimension n·(n+1)/2 s'il y a 1+n dimensions d'espace-temps. (Pareil: une 2-forme ou matrice antisymétrique.) Mais je digresse un peu, là. …
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@pianocktailiste … et c'est juste une astuce en dimension 3 de voir ça comme un 3-vecteur); d'ailleurs, même en dimension 3 ça marche mal avec les réflexions (dans un miroir, E est transformé en −E mais B en B, donc on s'aperçoit que ce n'est pas un vrai vecteur). …
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@pianocktailiste … On peut le voir de différentes manières (notamment comme une 2-forme, ou comme une matrice n×n antisymétrique… qu'on peut aussi imaginer comme une rotation infinitésimale, parce que les rotations, c'est pareil, en dimension n tu as n·(n−1)/2 dimensions, …
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@pianocktailiste Je n'ai pas d'explication toute écrite, mais c'est clair que le champ magnétique (qui en dimension n a n·(n−1)/2 composantes) n'est pas un vecteur, c'est juste une petite astuce en dimension 3 de le représenter comme tel. …
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… and here's the rest of it: pic.x.com/dFPmA3v90G
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… in 2011, combined with his complicated relation with his father led to Trump deciding to run for president.␤␤This sketch is mostly vanished from the Internet, but I think it bears watching again. Here's the first part: pic.x.com/3pBqnaJyb4
As part of his election night coverage in 2016, Stephen Colbert aired a 4min animated parody sketch titled ‘Trump Begins’ (a parody of ‘Batman Begins’) or ‘The Dawn of Donald Trump’ imagining how being roasted by Obama and Seth Meyers at the White House Correspondents' Dinner …
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This 2017 article by the ‘Guardian’ is an interesting read on the scientific publishing business in general, and Robert Maxwell in particular: theguardian.com/science/2017/j…
For no particular reason, let me remind everyone that Robert Maxwell, the father of Jeffrey Epstein's co-conspirator Ghislaine Maxwell, made a bunch of money in the lucrative business of scientific publishing, i.e., selling scientists their own work.
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But an interesting variation I didn't know is this: how dense can a subset of the plane be while never having two points at distance 1? The paper arxiv.org/abs/2207.14179 proved that its density must be ≤0.2470 (solving a question by Erdős, who had conjectured <¼). •3/3
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It's only known that it's between 5 and 7 (though it seems likely the correct value is 7, witnessed by a coloring a hex tiling). Showing that 4 colors are necessary is a fun exercise, and the lower bound was improved from 4 to 5 only in 2018 (to some amazement). •2/3
One of the most infuriatingly elementary open problems in mathematics is that we don't know the smallest number of colors required to color the plane so that no points at distance 1 have the same color — the famous “Hadwiger-Nelson problem”. •1/3 en.wikipedia.org/wiki/Hadwiger%…
I asked a MathOverflow question on what “usual” properties of topological spaces can be expressed internally in the topos of sheaves of that space (i.e., by saying that some statement ϕ holds in this topos): mathoverflow.net/q/507955/17064
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… The common theme is: you have a photo taken from an unknown point M, and you can see several known landmarks (A,B,C,D) on the horizon and maybe measure something about them: what does this tell us about M?
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③ Given four points A,B,C,D on the plane, what is the locus of points M such that the cross-ratio (MA,MB; MC,MD) of line directions is a given value?␤␤Meta-question: can we relate all three problems?␤␤…
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… (This first one I know: it's a[n arc of] circle.)␤␤② Given three points A,B,C on the plane, what is the locus of points M such that the ratio of angles ∡(MA,MB) / ∡(MA,MC) is a given value?␤␤…
The question of “how to identify a place from a few landmarks on the horizon” suggests three independent but similar geometry problems to me:␤␤① Given two points A,B on the plane, what is the locus of points M such that the angle ∡(MA,MB) is a given value?␤␤… x.com/gro_tsen/statu…
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Bon, la réponse (trouvée par deux personnes) est que c'était là: openstreetmap.org/?mlat=48.88005… sur les toits de l'immeuble dont l'adresse doit être au 46 rue Louise-Émilie de la Tour d'Auvergne. pic.x.com/zM1B1DeGuw
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La vidéo a été flipée. 😬 x.com/gro_tsen/statu…
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@cortisquared @Conscrit_Neuneu Switzerland has a super strong economy, and a reputedly functional democracy, yet one of the strongest far-right party in Europe.␤␤The rise of the far right is simply due to all people having lived through fascist régimes dying, and <insert the famous quote by George Santayana>.
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@Olive_Roussel Bien joué! 🥇
Mimosa (Acacia dealbata) in the Jardin des Plantes, Paris, today. pic.x.com/IVepBYb1Eu
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@ZeitblomS Ah ben oui, c'est sûr que ça change complètement! Si je cherchais un endroit depuis lequel on voit la tour Montparnasse, le Panthéon et les tours du 13e sous un certain angle approximatif, et si on inverse la vidéo, ça change beaucoup l'endroit! 😂
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@Didier515 x.com/gro_tsen/statu…
RT @ValDelamere: the Italian guy is German and the German guy is Italian what's going on here pic.x.com/E081LyhxgW
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Pourtant, juste par le fait qu'on voit la tour Montparnasse, le Panthéon et les tours du 13e à l'horizon, on devrait pouvoir retrouver l'endroit.
Je viens de passer un temps invraisemblable à essayer de jouer à GeoGuessr pour identifier où exactement, dans Paris, a été filmée cette petite scène, mais je suis vraiment mauvais à ça: reddit.com/r/SweatyPalms/…
So, the “Roaring Twenties” en.wikipedia.org/wiki/Roaring_T… refers to the 1920's decade, but the “Roaring Forties” en.wikipedia.org/wiki/Roaring_F… refers to the westerly winds around latitudes 40°–50° south. This is not at all confusing.␤␤#ContextClub
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@JacqBens … Of course, it's also disappointing that a standard font should be missing the character in the first place, considering that the list of space characters in Unicode isn't that huge, and they're not exactly hard to draw. 😁 (This character is… 26 years old!)
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@JacqBens I haven't used Windows in about 30 years, so I can't really comment, but I'm surprised that if the font doesn't have a character it displays as tofu rather than fall back to a similar font which has it (not ideal, but still better than a block). …
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@JacqBens … And as far as I know (disclaimer: I've never actually checked thoroughly), the only Unicode space that satisfies these two criteria is U+202F NARROW NO-BREAK SPACE.␤␤This is indeed what I tend to use in this context (I didn't know Windows did anything of the sort).
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@JacqBens … Second: what kind of space to use? Well, this isn't exactly specified by these standards, but you can argue: you want this space to be unbreakable because you don't want to split a number, and you want it to be thinner than a full space to avoid confusion. …
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@JacqBens It is indeed reasonable.␤␤First: separating digits in groups of three by inserting some kind of space is standard in many countries, including France, and is also recommended by international standards such as ISO 31-0 and CGPM22 (2003) resolution 10 bipm.org/en/committees/… …
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@xmoisant @pbeyssac La page liée dit: «ce produit n'est plus dans notre gamme». pic.x.com/gA1kHY0hHH
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Le fabricant lui-même (qui a quand même intérêt à vendre son produit) n'est même pas foutu de mettre en place une page Web avec l'EAN et les coordonnées des grossistes qu'il fournit.␤␤Un tel niveau d'incompétence et de nullité me laisse quand même sans voix.
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Chaque produit à un EAN, donc il doit y avoir plein de fichiers qui ont ce numéro comme clé principale, mais si je recherche 3760056265842 dans Google google.com/search?hl=fr&q… ça renvoie trois malheureuses pages qui ne disent rien du tout.␤␤COMMENT EST-CE POSSIBLE?
Toutes autres choses mises à part, je trouve ça complètement dingue qu'à une époque où absolument tout est informatisé, il n'y ait aucun moteur de recherche des produits en supermarchés, aucun moyen de savoir ce qui se vend où, sauf à aller en personne dans les rayons. 🤦 x.com/gro_tsen/statu…
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Si vous trouvez où en acheter, ça m'intéresse. Même si ce n'est pas un endroit où je peux réalistement aller, ça me donnera une idée de si ça existe encore, quel type de chaîne de grande distribution en a, etc.
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Ce sont des bouts de fromage cuits au four, vendus en sachets de 60g. Il y a deux saveurs: nature et tomate-origan. Ça peut se trouver au rayon apéritif, chips, fromages, ou même avec les croutons pour salade. Ce n'est pas conservé au frais.␤␤casa-azzurra-italia.fr/casa-azzurra-q…
Mon grignotage apéritif préféré, les «croquants de fromage» de la marque Casa Azzurra (EAN: 3-760056-265842), ont de nouveau disparu du seul magasin où je les trouvais. 😭␤␤Si vous les voyez en vente qqpart, faites-moi signe SVP! pic.x.com/M8GNr4pDOI
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@SimonArchipoff @Jilcaesel Je suppose que les gens (susceptibles de menacer le personnel) à qui s'adresse ce message savent à quoi ressemble une clé de coffre.
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OK, the paper seems to conclude that the likelihood of the event happening by random tunneling is something like 10⁻²⁰⁰ per year, so don't lose too much sleep over this. Still my favorite doomsday scenario, though.
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… And, yes, if the electroweak vacuum turns out to be metastable and a seed of a more stable vacuum appears somewhere in the Universe, this is Very Very Bad, as the vignette of the video youtube.com/watch?v=ijFm6D… suggests. …
I love this ever-so-slightly worrying graph from the paper “Vacuum Stability and the Higgs Boson” by Jose R. Espinosa arxiv.org/abs/1311.1970 suggesting that the top quark mass is ever so slightly too large for the vacuum in our universe to be completely stable. … pic.x.com/KbSFPitFXJ
Tact is the art of making a point without making an enemy.
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@archiptere @laurentbercot … Ça a pris 1–2 ans, je dirais. Mais je suis d'accord avec Laurent que BS n'est pas la panacée, et je comprends que des gens ne veuillent pas y toucher de peur que ça finisse exactement pareil, et préfère Fd. J'ai écrit ce fil de comparaison: bsky.app/profile/gro-ts…
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@archiptere @laurentbercot … À ce point, j'en suis à 1.9k followers sur BS, mais comme le modèle d'abonnement est différent, j'ai retrouvé grosso modo le même niveau de conversations, et bcp de mutus que j'aimais bien. (L'interface est hyper semblable, aussi, à qqs détails près.) …
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@archiptere @laurentbercot … J'ai commencé à poster l'essentiel des choses en double, d'abord dans le sens X→BS (plus facile parce que la limite de caractères est plus sévère ici), puis BS→X en retirant qqs mots au besoin au passage. Et quelques annonces 🔽 au passage. … x.com/gro_tsen/statu…
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@archiptere @laurentbercot Mon expérience de la migration Twitter→BS, pour ce qu'elle vaut:␤␤J'ai ~7k followers ici, donc aussi un certain frein à partir (pas vraiment pour les vues, mais pour les interactions avec certains comptes que j'aimais bien). …
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@JacqBens C'est le dual de «la bave du crapaud n'atteint pas la blanche colombe». (Il n'y a pas vraiment de contexte.)
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@Jilcaesel Les clés des coffres bancaires (ou au moins un modèle fréquent de telles clés) ont une forme assez spéciale, je ne sais pas si c'est ce que tu observes.
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@laurentbercot @archiptere Pour BS↔︎Fd, c'est hyper facile, il y a un bridge fait pour. Forcément, il y a des limitations et des choses qui passent mal, mais c'est un bon compromis.␤␤Pour X, perso je fais surtout du copier-coller depuis BS: comme BS a une option «copy post text» commode, ça va très vite.
«La fiente du pigeon n'adhère pas à la verte grenouille.»
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… So you describe the thing to the AI and ask it “what's the standard term for this?” — of course you should never trust the answer, because it might be a hallucination, but now that you have a term or phrase to search, you can google it to confirm.
I'm really not a fan of LLM AIs, but one area where they do shine is when you're looking for a word or phrase or standard term for something and can't find it after much googling or going through a dictionary of synonyms. …
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I think mathematics tends to shy away from Ⓒ compared to other sciences, especially when it comes to inventing brand new words (not just tacking a prefix on an existing one, like “ultrafilter” or “paracompact”), but a serious study would be interesting.
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The above examples are from mathematics, but the idea applies to any domain, of course. I wonder if anyone tried to do some stats to see how these three modes of naming are used in function of the epoch and academic domain.
There are 3 main ways to create scientific terminology:␤␤Ⓐ Use someone's proper name (e.g. “Euler circle”, “Fourier transform”).␤␤Ⓑ Repurpose an existing word (e.g. “field”, “compact”, “sheaf”).␤␤Ⓒ Invent a new word, often from existing roots (e.g. “ultrafilter”, “totient”).
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Tweet IDs are: 2017430777462415782 and 2017646233381228780 if you really want to check them. (But seriously: don't.)
Poe's law in action: it is now absolutely impossible to decide what is satire and what is not. pic.x.com/uwt0eEiekn
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I got a very elegant and simple answer: mathoverflow.net/a/507736/17064␤␤So it turns out that if we can computably perform any f-oracle and a g-oracle program computations, provided they both terminate and yield the same result, then in fact one of f or g is computable. Remarkable!
Mankind loves the “tower of Babel” myth so much that we pretty much replayed it in the computer world: aim for the sky, and end up with a gazillion confusingly different languages. But we didn't need the wrath of God for that: we did it all on our own. 🤓
RT @TerribleMaps: Language groups in Western Europe pic.x.com/Xpw5Y1k9K6
RT @ngspiensfr: Il y a une Encycopaedia Universalis, apparemment complète ou pas loin, en « servez-vous » dans la laverie près de chez moi.…
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… Yes, writing sociological drama is hard, and so is writing a historical epic. But they didn't even try. They even go as far as finding tricks to make characters reusable for centuries.␤␤The Smurfs is a better adaptation of Marx's ‘Das Kapital’ than this series is of Asimov.
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… Idiots complain about the series having changed the gender or skin color (unspecified in the books, btw) of this or that character, but fail to note that, beyond the massive changes in plot, the major problem is the utter betrayal of Asimov's main idea. …
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… going to adapt a work of this kind to the screen, you should at least try to honor its core idea.␤␤Apple TV's series (or the part I have seen) fails utterly. All is centered around character drama. We are given NO insight on the galaxy's masses: sociology, politics, etc. …
The ONE CENTRAL message of Asimov's ‘Foundation’ saga is that History is not shaped by the choices of single individuals but by their aggregate actions.␤␤Admittedly, Asimov himself struggled with that premise, and it may not be true in real life. But still, if you're …
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(Ok, yeah, and Alexander Skarsgård is impossibly sexy. That too. 😅)
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So, I saw ‘Pillion’, and I really enjoyed it. Despite what the poster and title might lead one to believe, it has very little to do with motorcycles. It is, however, a very powerful reflection on what a relationship is, and how our intimacy relates to our public persona.
RT @aufek: I'm begging you; no matter how extreme the demoralization gets you must absolutely not abandon your belief in good.
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@laurentbercot Quelqu'un me signale que son compte est peut-être suspect: mathstodon.xyz/@glocq/1159971… — personnellement je suis incapable de trancher.
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@mahdi_tcs_ These aren't cheap cables: I've had the problem with several fairly high-end brands, including Rampow.␤␤And even if they were, I never had problems with my micro-USB cables, no matter how cheap the brand, so there is a clear regression for me here.
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@mahdi_tcs_ I've had the problem with several different cables, from different vendors, and it's not the device because changing the cable fixes it.␤␤And I'm not the only one as reddit.com/r/UsbCHardware… and electronics.stackexchange.com/questions/6853… and quora.com/How-do-I-fix-m… show.
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PS: for vintage masterpieces of the “pixel art” fantasy æsthetic I'm talking about, check out effectgames.com/demos/worlds/ and effectgames.com/demos/canvascy… — beautiful pixel art images by Mark J. Ferrari animated purely by palette cycling (and here recreated in HTML5).
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Here's another example, by a different artist (Andreas Rocha), in the same style: deviantart.com/andreasrocha/a… x.com/gro_tsen/statu…
There is probably a name to be given to this artistic style, which is not pixel art, but somehow still reminiscent of the æsthetic that the background stills of fantasy adventure genre computer games of the 1990's was trying to go for. x.com/gro_tsen/statu…
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Or this one titled “Journey 3”: artstation.com/artwork/OyeEmJ
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Like this “Quiet border Town” landscape: artstation.com/artwork/g0JwNL
Despite some overused clichés, much of the artwork of this “pixel cat” digital artist really resonate with me: artstation.com/pixel-z
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USB-C is basically a modern reinvention of all the annoyances of SCSI: now there are a gazillion different cables, speeds, voltages, etc., and it's an impenetrable mess so the only thing you can do is plug'n'pray!
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Seriously, the selling point of USB-C was that, so long as it fits, it's supposed to work whichever way you plug it in, and in my experience this is emphatically NOT TRUE.
Before USB-C we had to try 2 or 3 different cable orientations before finding one that works.␤␤Now with USB-C we still have to try 2 or 3 different cable orientations but now it's even harder to tell when one doesn't work, because there's no physical obstacle. 😡
Sait-on de quelle maladie Louis XV a failli mourir en 1744 (à Metz)?
Reminder: all that is AI is fake, but not all that is fake is AI.
I asked a computability question on MathOverflow about a condition on f,g:ℕ→ℕ that says roughly “anything that can be computed from f and g separately with the same result can be computed directly”: mathoverflow.net/q/507625/17064
Un nouveau rant (pas trop interminable cependant) dans mon blog sur la manière dont l'écosystème Linux ressemble à un puzzle dont on ne comprend pas comment les pièces s'emboîtent, et le fait qu'un tout petit peu de doc pourrait aider grandement: madore.org/~david/weblog/…
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Two interesting videos analysing the way modern Hollywood movies look too clean, too perfect, and, as a result, unrealistic: youtube.com/watch?v=BzKXF0… (on actors being too beautiful) and youtube.com/watch?v=tvwPKB… (on the lack of “haptic feel” to them).
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@GillibertLuc <takes notes>
How is France so high on the list? Are we still not arrogant enough? x.com/Globalstats11/…
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(Your next mission is: dicover Ursula von der Leyen's favorite color! Adventure! Excitement! Suitable for kids all ages.)
To be fair to the US House of Representatives, trying to find anything on an EU institutional Web site is a bit like an RPG game, with dungeons, dragons, traps and (sometimes) treasure at the end. So let's congratulate them on the XP gained. 😁 x.com/FrenchResponse…
Some beautiful projections of the first shell of the 24-dimensional Leech lattice: 🔽 x.com/misaki_ohta_/s…
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@misaki_ohta_ Very nice! These are all varying projections of the first shell of the Leech lattice?
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I think I'm going to print this comic and stick it on the door next time I encounter this sort of situation: wumo.com/wumo/2026/01/29 [Wumo comic for 2026-01-29] pic.x.com/kptR7lw2Ws
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@EvarixGaulois Non, malheureusement, je ne sais plus où j'ai lu ça.
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By “shmork”: x.com/i/status/19196…
New plushie alert! pic.x.com/RnQFOootPt
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Explications plus détaillées sur ce que je veux dire ici: reddit.com/r/france/comme…
Opinion polémique: à chaque fois que vous voyez un «graphique de base 100» (p.ex., en économie), c'est que ça devrait, en fait, être un graphique en échelle log. Il n'y a aucune raison valable pour faire un graphique de base 100 au lieu d'un graphique en échelle log.
RT @2020Marceau: Vérification d'identité numérique 🪪 🆔␤7 jours pour 😭␤␤Personne ne mesure encore toutes les conséquences du moindre vol de…
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C'est une sorte de récapitulatif de ma position dans la discussion Bluesky suivante: bsky.app/profile/did:pl…
Un billet (pas trop long) où je me plains du fait que les gens compilent de moins en moins les programmes Linux à partir du source, et du coup ça devient de plus en plus difficile, et on se trouve dans une situation que j'appelle le «clopen source»: madore.org/~david/weblog/…
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@gine_robert @pianocktailiste C'est vraiment une condition complètement conne: c'est pas comme s'il y avait tellement de femmes scientifiques françaises mortes avant 1789 qu'on doive imposer la limite parce qu'on manque de place. En fait, ça ressemble presque à un critère exprès pour exclure Mme du Châtelet!
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A mini-documentary about Belgian architect Victor Horta and the origins of Art Nouveau — with views of absolutely stunning mansions in Brussels that he designed: youtube.com/watch?v=k20doH…
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Voilà: ⬇️ pic.x.com/AjIlICwlkk
RT @Poulin2012: Il est faux de parler "d'interdiction des réseaux sociaux aux moins de 15 ans", en réalité, c'est une loi "d'obligation d'i…
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@EvarixGaulois La notion d'énergie était extrêmement confuse à l'époque, entre les «partisans» de m·v et les «partisans» de m·v². Émilie du Châtelet a grandement contribué à lever cette confusion en montrant que m·v² a de l'importance même dans un choc inélastique.
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Je rappelle qu'on a renommé la «place de la Barrière d'Enfer» en «place Denfert-Rochereau» (en l'honneur de Pierre Philippe Denfert-Rochereau) en 1879, donc ce genre de récupération onomastique est parfaitement possible.
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Ou au moins, si c'est trop compliqué de renommer officiellement la voie, de mettre en-dessous sur les plaques «Émilie Le Tonnelier de Breteuil, marquise du Châtelet (1706–1749), mathématicienne, physicienne et femme de lettres française».
Bon, je vais vraiment me fendre d'une lettre à Anne Hidalgo proposant de renommer la place du Châtelet en place «Émilie du Châtelet». x.com/gro_tsen/statu…
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Ceci étant, je ne comprends rien aux critères de la liste. Soit c'est juste des françaises, et alors R. Franklin est incongrue (elle a juste passé qqs années en 🇫🇷, je crois), soit c'est le monde entier, et alors elle omet plein de femmes scientifiques de plus grande envergure.
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Non mais sérieux, prétendre compiler une liste de grandes femmes scientifiques françaises(?) et omettre celle qui a éclairci la notion d'énergie et pressenti sa conservation, c'est vraiment un exploit. 🤦 fr.wikipedia.org/wiki/%C3%89mil…
ILS N'ONT PAS MIS LA MARQUISE DU CHÂTELET DANS LA LISTE!!! 😭 x.com/LeParisien_75/…
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@Sotorumuro Well, as my dictionary excerpt shows, native English speakers do pronounce two syllables in the second word of “bona fide”, or at least, did this when this dictionary was researched.
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(And yes, I know I'm fighting for a lost cause. The view from this hill is beautiful: please prepare a nice little burial place for me there. I want the words “he was a bona fide warrior” on my epitaph.)
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From Longman's “Pronunciation Dictionary” by J. C. Wells: pic.x.com/GhsolrCoJ3
✱ PSA: If you say “bona fide” pretty much like “bonified”, you are a bunch of ignorami. 😜␤␤No, seriously, “fide” has two syllables in Latin. Say it like “fee-day” in English. I can tolerate “feye-dee” on a good day, but if you think it rhymes with “mystified”, please stay away.
It would appear that the phrase “happy few”, while presumably coined by Shakespeare (in Crispin's day speech from ‘Henry V’) is currently far more popular in French than in English, possibly due to Stendhal's influence. pic.x.com/B4fCAnQ9b8
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This one is in French, for a change: the story of the “galerie des machines” that was constructed for the same 1889 World Fair as the Eiffel Tower — how it was built, what it was used for, and how it came to an end. youtube.com/watch?v=qLOxwP…
RT @SaarelaHC: Highland Cattle photo of the day pic.x.com/86aSUl6WcG
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[…] Well, that's what this building says for Toronto. You've got a headmarker for a grave and future generations will look at it and say: ‘This marks the spot where Toronto fell.’”␤␤(Cited in: Allan Levine, ‘Toronto: Biography of a City’, chap. 8, p. 213.)
Today I learned that when the new (and now iconic) Toronto City Hall building was designed in 1958, the 91-year old cranky Frank Lloyd Wright was not a fan. He commented: “Every graveyard in Canada, if it could speak, would say ‘amen’ to the slab of [this City Hall]. […] pic.x.com/byAYSVqaf7
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*United States␤␤A great book, by the way, which I highly recommend.
Historian of fascism Robert O. Paxton, writing in 2004 about the possibility of fascism in the Untied States, in ‘The Anatomy of Fascism’ (chapter 7, page 202): pic.x.com/MaedxtDHqN
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Ah, so apparently the answer is that we need to quote words in the search if there are ≥3 and we want them to actually appear in the results. Good to know. x.com/grok/status/20… pic.x.com/pngF1RqyJn
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Should I file it under “this is another basic feature that only Premium® accounts get” (i.e., are blue check people allowed to do 3-word searches? @JacqBens, could you tell me?) or just “Elon Musk broke everything”?␤␤(I'm positive it used to work fine.)␤␤@grok, a comment?
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My examples were: x.com/search?q=compu… versus x.com/search?q=compu…
So apparently now when you do a Twitter search for just TWO words it gives you accurate results, but if you try to go for THREE it gives you random junk very vaguely related to the search words or not at all. pic.x.com/7MovRkicDr
RT @TerribleMaps: Which Mexican country is your favourite? pic.x.com/W7kK01GTSf
I'd like to comment how the “μολὼν λαβέ” (“come and take it”) people have become rather “λαβὼν μόλε” (“take it and go”), but I'm afraid my chances of getting the right imperative aorist of βλώσκω are slim and almost nobody would get the joke anyway.
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“Sociologically” isn't the word I want. I mean it reveals a lot about the way mathematicians think about mathematics, how we conceptualize things.
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Link to said discussion: mathoverflow.net/q/507049/17064
The ongoing discussion on MathOverflow on whether it is possible to define the trace of a linear map (on a finite-dimensional vector space over a field) without “picking a basis” — or what this phrase even means — is mathematically and sociologically fascinating.
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(For example, when I want to enter the character ‘−’ [U+2212 MINUS SIGN] or ‘ő’ [U+0151 LATIN SMALL LETTER O WITH DOUBLE ACUTE] I need to copy it from a Unicode app. Why can't I just add them to the keyboard popup boxes? 😡)
I find it absolutely infuriating that Google's Android keyboard “Gboard” doesn't offer any means to add custom symbols to the layout. Is there a fork that allows this?
Still confused as to why so many people are suddenly saying the German Intercity Express trains are horrible and should be abolished. 🤔 pic.x.com/J1nJrQkzP6
RT @allenanalysis: Scottish comedian Lewis MacLeod just did a Donald Trump impression so accurate it feels like evidence. https://t.co/g2Ud…
RT @Naturalphilosy: “Perfection is insane. The entire tyranny of the perfect body, the perfect family, the perfect life is literally a comm…
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@GenevieveMadore Les chiffres pour les haricots rouges ne collent pas avec afcd.foodstandards.gov.au/fooddetails.as… (qui est une source fiable): 14g de protéines, 10g de fibres, 2mg de fer, 10mg de calcium et 15mg de magnésium pour 100g. (Ceux de la viande rouge sont à peu près OK, cf. afcd.foodstandards.gov.au/fooddetails.as… ).
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I mean… COME ON! 😂 youtube.com/watch?v=81wyj6… pic.x.com/1Nop9aQLk0
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@Jilcaesel OK, well, I've stopped believing that anything makes sense on this site.
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He-Man is canonically gay, and he is fa-bu-lous. Deal with it.
I hear there's a He-Man (“Masters of the Universe”) movie to be released soon, and I hereby wish to declare that if He-Man isn't depicted as having a fabulous gay dom/sub romance with Skeletor, it isn't canon.
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… So the only way I've found of recompiling my Armbian kernels is to have a dedicated virtual machine running under qemu whose only purpose is to run the MSTDE. (Admittedly, it works. But it takes ages. And if something were to go wrong, it would be undebuggable.)
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… And one of the things the Magical Script That Does Everything does is (🚨 I kid you not 🚨) it wants to run ntpdate to set the (compilation host) system clock to date so as to precisely time the compilation (🤦 ). So it needs to run as root (😱). …
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… No other way of compiling Armbian is supported. You can't even easily checkout the kernel tree without the MSTDE. You can't merely change a config option without committing your config to a Git tree and running MSTDE. You need to let it do its thing exactly as it wants it. …
Reminds me: did I already mention I have NanoPi boxen that run Armbian? Now Armbian is great as long as you don't need to recompile the kernel. If you do, you discover that it is not like a usual Linux kernel: you need to run the Magical Script That Does Everything (in zsh). … x.com/gro_tsen/statu…
The Alsace region of France should be shown in blue. x.com/amazingmap/sta…
RT @LindyTasteful: The report of Trump's first visit to Japan is a must read pic.x.com/S0vRZwyHmF x.com/alx/status/201…
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‣ Everything happens in automagical programs like “cargo build” or, worse, tailor-made compile scripts. Which simplify things IF ALL GOES WELL. But if you hit a snag, or if you have a slightly unusual setup (even just “don't pollute my homedir! 🙏”), well — good luck! 😢␤␤•3/3
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‣ Because all binaries are provided prebuilt or, worse, as Docker images (🤮), there is no incentive to fix this dependency hell, neither at the source (“just get the compiler as a binary”) or at the target (“just don't bother building from source!”).␤␤… •2/3
Compiling pretty much anything under Linux has become an absolute nightmare. 😡␤␤‣ Everything has a zillion build dependencies with incredibly stringent constraints (like “we want Rust version 1.92.0 exactly — no more no less”).␤␤… •1/3
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@Jilcaesel Anyway, thank goodness for `jq -r '.data.threaded_conversation_with_injections_v2.instructions[1].entries[2].content.itemContent.tweet_results.result.legacy.entities.media[0].ext_alt_text'` 😆
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@Jilcaesel (Or maybe this isn't so new after all, and the Web interface only shows you the alt-text on your own images, so I just thought I was the only one still using it. Anyway, typical Musk-brand crappiness.)
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@Jilcaesel Oh great: the enshittification of Twitter continues further: the Web interface seems to no longer let me see alt-text; and the Android mobile interface displays it in a non-selectable way (this one isn't new).␤␤But I'll manage, thanks.
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So the answer is: yes, it is a world of pain and suffering, but I eventually figured it out: pic.x.com/kRIVT2Hd2V
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@Jilcaesel Oh that could be super useful (even if for this particular symbol I'll do otherwise)! Thanks. Could you dump that code in text form somewhere?
RT @kareem_carr: man: i wish to publish␤␤reviewer 2: your paper is no good␤␤man: i'll do anything to improve␤␤reviewer 2: it's simple. you… x.com/apagliar/statu…
RT @DarkVador_Off: Vous ne verrez rien de mieux aujourd'hui...␤␤(Via @ComplotsFaciles sur FB 🖤)␤␤#Trump pic.x.com/NBiWhyZ9NQ
Suppose I want to use the om sign 🕉︎/ॐ as a mathematical symbol in pdfLaTeX (not XeTeX / LuaTeX). Am I entering a world of pain and suffering or is there a way to do it?␤␤(I didn't find it in the comprehensive LaTeX symbols list, but it's hard to search this document.)
RT @mikenelson586: But Doctor, I am Pagliarini x.com/apagliar/statu…
RT @AMNH: Have you ever seen a pink grasshopper? A genetic mutation called erythrism (the overproduction of red pigment) leaves some indivi…
RT @Number10cat: It's hard to explain just how badly Trump has messed up that British people now view the President of France positively. x.com/emmanuelmacron…
J'ai publié sur mon blog un rant (que je me promettais depuis longtemps d'écrire) sur la notion d'intelligence (naturelle), la question de sa mesure, et ce qu'on essaie de vous vendre quand on vous en parle: madore.org/~david/weblog/…
Pro-tip: le 21 janvier, quand on voit des gens porter le deuil de Louis XVI, on peut leur demander s'ils commémorent ainsi la mort du camarade Lénine.
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@JacqBens Well, we agree on this point, then. 😁
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… mais c'est parce qu'il y a du relief ― et c'est pas la direction de Paris ― mais c'est la direction de Meaux ― mais c'est trop étendu en largeur pour être une seule ville, et puis c'est rouge ― mais non, c'est orange comme la vapeur de sodium, et ça bouge pas ― etc.» pic.x.com/S1zS9usmC1
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Bon, on a probablement vu quelque chose, mais c'était un peu underwhelming: on a passé tout notre temps à débattre «si, si, c'est une aurore boréale ― non, c'est juste de la pollution lumineuse ― mais non, c'est trop haut dans le ciel, ça part pas du sol ― …
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Évidemment, c'est vers le nord que c'est le plus couvert. 😠
Le poussinet et moi tentons d'aller sur la butte de Doue (en Seine-et-Marne) voir si on aperçoit l'aurore boréale loin de la pollution lumineuse de Paris.␤␤(Je sens gros comme une maison qu'on va faire 1h de route dans chaque sens pour ne rien voir du tout.)
“Woe to thee, O land, when thy king is a child.” (Ecclesiastes 10:16)
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@monsieurpuyo Exactly: x.com/gro_tsen/statu…
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Somewhere, somehow, somewhen, the chief editors of ‘The Onion’, ‘Der Postillon’ and ‘Le Gorafi’ and others found a magical lamp with an evil genie in it, and didn't think carefully enough before phrasing their wish to come up with more realistic stories.
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Nine years later: x.com/gro_tsen/statu…
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legorafi.fr/2017/04/14/tru…
In 2017, the French satirical news site ‘Le Gorafi’ ran this story: “Trump says he is prepared to bomb until he is awarded the Nobel Peace Prize” and imagined him saying “I don't know how many deaths it'll take, but I'll get that prize”. 😅 pic.x.com/HpMozNJf8E
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@SamuelDamoy x.com/gro_tsen/statu…
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PPS: Støre has confirmed that the letter shared on social media (above) is a genuine message he got from Donald Trump (and also that he repeatedly explained to him that it's not the Norwegian government that awards the Nobel prize 😂). vg.no/nyheter/i/q6Ad…
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PS: not that it matters in this post-truth world, but regarding “no written documents”: govinfo.gov/content/pkg/ST… pic.x.com/Mu8Ezc3GLm
“Didn't get my Nobel 😡😭 so I can make threats now! And as a proud American, I reject the absurd idea that ‘boats landed here centuries ago’ gives you rights. So anyway, Denway, nice Greenland you've got there, it'd be a shame if something were to happen to it. Sincerely, DJT.” x.com/nickschifrin/s…
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Oh yes, and selling California would definitely be a way to show you OWN THE LIBS living there (who, I am told, are not the best: they're bringing drugs, they're bringing crime, they're rapists, and some, I assume, are good people).␤␤Think of all the advantages!
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Not to mention: selling California to Denmark would be a HUGE deal, a TREMENDOUS deal, the likes of which we've never seen before, proving the AMAZING business acumen of whoever did it.␤␤And I've heard it would certainly be worthy of a prestigious ✨FIFA prize in Economics✨!
I think this should be sugar-coated with the reminder that if Trump sells enough blue states to the EU (or Canada), he can pass a constitutional amendment to remove term limits and pretty much guarantee he becomes president for life.␤␤(See the subtle art of the deal here?) x.com/NoLieWithBTC/s…
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Similarly, it's a myth that the ancient Greeks couldn't see the color blue, but it's absolutely true that heraldry nerds don't see color like normal people do: they see “azure” and “gules” and stuff, which I'm sure must be some shades of ultraviolet and infrared.
It's a myth that Inuits have 100 different words for “snow”, but it is absolutely true that vexillologists have 100 different words for what every sane person will just call a “flag” while they angrily explain to you that it's an “ensign” or “standard” or “banner” or whatever.
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To be fair, I'm sure one day or another Musk must have said “it looks like it's going to rain today” and it did — and Wikipedia editors didn't list it as an accurate prediction, so muh bias.
The real reason Musk hates Wikipedia so much: x.com/JE_dna/status/…
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(Jokes usually don't have an identifiable source, but this quip sounds like it could be, say, by Groucho Marx or W. C. Fields or sbd like that. But strangely enough, the Internet, usually so keen on providing dubious attributions to witty quotes, doesn't seem to have this one.)
Does anyone know the source of the joke: “I must have a lot of talent because I've never used any”?
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I'd say it takes an LLM to invent such a haphazard mix of actually good (if banal) advice, conservative bullet points and undiluted wtf, but no, this list seems to have been circulating for longer than that.
This list of ‘99 steps toward MANHOOD’ may truly be the most bizarrely random multifarious conglomerate I have ever seen. How do you start a list with “trust Christ as Lord” and end up putting stuff on it like “don't wear crocs”? 🤣 pic.x.com/8RahY1pIF5
What your TL needs right now is the Star Wars Imperial March played on rubber chickens: youtube.com/shorts/PQhVtfH…
La carte des endroits où j'ai pris une photo me fait de plus en plus penser à la mesure de la fonction d'onde d'un objet quantique: à force de répéter les observations, comme ça, on va commencer à voir émerger des franges d'interférence. pic.x.com/D5rgBIsM9Y
This seems to be making the rounds: pic.x.com/zGn2WaKoab
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… “Excuse me, but what is the Serre group?”␤␤That person was Jean-Pierre Serre.
Apropos the annoying habit mathematicians have of naming mathematical objects after people, a little anecdote:␤␤I once attended a talk during which the speaker mentioned the “Serre group”. en.wikipedia.org/wiki/Serre_gro…␤␤An elderly man in the front row raised his hand and asked: …
RT @ryangrim: Funniest version of free speech absolutism yet x.com/elonmusk/statu…
OK, new proposal!␤␤Rather than letting the US or Denmark have Greenland, how about we divide it between Spain (west) and Portugal (east) along a meridian, say, 370 leagues west of the Cape Verde islands?␤␤(I'm sure nobody thought of that before.)
This is an actual official French government account trolling the Russians. 🤣 x.com/FrenchResponse…
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I'll give you the TL;DW. What should Europe do? Seriously invest in defending Greenland, e.g., by stationing European soldiers there. Which might very well be exactly what the US is trying to goad Europe into doing, and, no, this isn't just a Trump thing.
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I emphasize that this guy is an actual academic, specializing in game theory, crisis bargaining, geopolitics, strategy and international relations, and who regularly talks to NATO officials: he's not your average journalist or political pundit. The difference in PoV is striking.
Anyone interested in the “US annexing Greenland” situation (or what Europe should do to respond to the threat) would be well advised to watch this 20′ video by geostrategy and international relations expert William Spaniel (aka “Lines on Maps”): youtube.com/watch?v=4bHHPN…
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So apparently if you ask ChatGPT “what is the seahorse emoji?” [this emoji, in fact, does not exist] it can cause it to enter a kind of crazy loop, and the reason is somewhat interesting: youtube.com/watch?v=W2xZxY…
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In essence, this is about whether the curves in this picture and related ones actually cross (I suspect they never do): x.com/gro_tsen/statu…
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Sorry, link is here: math.stackexchange.com/q/5119337/84253
I asked a question on Math StackExchange about whether 0 is a critical value of the Fourier transform of a plane regular (2n)-gon.
RT @FFmpeg: Yes, it's like saying there's no need for furniture craftsmen because IKEA furniture exists. x.com/baianoise/stat…
“Central bankers are liked whipped cream: the more you whip, the tougher they get.” —Wim Duisenberg, former president of the European Central Bank x.com/federalreserve…
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@arivero Oh yes, absolutely. x.com/gro_tsen/statu…
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@cspaliwa1 I'm not saying I'm not smart, I'm saying there are a gazillion many different ways of being “smart”, I am some of them, not at all others (or even downright stupid in some), and IQ scores measure an arbitrary and pretty meaningless combo of these smartnesses.
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Maybe fill it with pronouns. This seems to be the American conservatives' kryptonite. For some reason they can deal with other parts of speech, but pronouns they're mortally terrified of. And Danish has so many pronouns, I'm sure they can spare a few.
How about this?␤␤We let Donald Trump take Greenland, but before Denmark steps away, we leave a BIG BEAUTIFUL HORSE, the likes of which the world has never seen before, as a present to the Americans.␤␤There's no way Trump will beware of Danes bearing gifts.
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@Jilcaesel @Mlambm @davidbessis “But muh large body of research shows correlation” and “we named it ‘g-factor’ so it must make sense”. 😆 x.com/gro_tsen/statu… pic.x.com/WfyUZbwEsh
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@insights198 So the idea that you can deduce something about innate talent by observing the effects on success (e.g., that the rich are more talented than the poor) is a form of the just world fallacy.
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@insights198 Because History (whether at the individual or collective level) is not a deterministic phenomenon, and small random differences cause discrepancies that accumulate. There has even been some modelling of such effects: arxiv.org/abs/1802.07068
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@lu_sichu … So, yes, in this situation, the only way to prove the effect would be to do some kind of randomized blind test instead of a population measure. And good luck with that.
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@lu_sichu … So when the observation you make just happens to neatly align with the obvious confounder which you try to control for, the simplest explanation is that the confounder wasn't properly controlled for, not that some true effect just-so-conveniently happens to align with it. …
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@lu_sichu I'm not saying that there aren't differences in distribution of abilities, I'm saying that we have absolutely zero idea what they are (not even their sign), and no way to measure them, because the ill-defined signal is drowned in extremely obvious confounding factors. …
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@insights198 … happens to neatly align with obvious sociological categories which would be gigantic confounders for the ill-specified phenomena you are trying to measure (and, for some reason, “in the US”? who ever said something about the US?), it's a waste of my time to go down this path.
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@insights198 … But if you want to live in the delusion that “development” of societies somehow lets us say something meaningful about the genetic abilities of the people constituting these societies rather than about the law of accumulated advantage, something which JUST SO CONVENIENTLY …
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@insights198 Quite the contrary, a neat correlation with obviously visible traits (e.g., skin color) and sociohistorical variables (“Africa”/“Eurasia”) suggests that they are the overwhelming factor. Genetics would suggests something messier, with, e.g., the Basques being aside. …
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@insights198 When there is a huge correlate in a measurable quantity, trying to subtract that correlate to get a signal is scientifically futile. When we don't even know what the quantity means or what the test is trying to measure, it is doubly futile.
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@insights198 I mean the experiment has to be done blind. This is a standard scientific practice: the experimenter shouldn't be able to tell which group the subject is in before the unblinding step.
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@insights198 @marclebel @davidbessis @Mlambm … so yes, this experiment is probably impossible to do (but I don't even know why we would want to or care about it), but if someone tries to argue they can measure the effect with less, they are probably trying to sell you a cryptocurrency or something.
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@insights198 @marclebel @davidbessis @Mlambm … so, take a random sample from your populations and have them raised in random sociological conditions, and make sure the people taking the test can't tell which population is which before unblinding. Anything less is scientific fraud, …
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@insights198 @marclebel @davidbessis @Mlambm If the hypothesis you want to test is that there are human populations with distinct intellectual abilities, and the only test you have is one which measures something ill-defined with probable huge sociological correlates, your only option is a randomized blind test, …
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@insights198 @marclebel @davidbessis @Mlambm I'm not saying it rules it out, I'm saying it's futile to try to prove it that way. Precisely because the different level of development introduces a huge bias in the quantity you're trying to measure (which you can't even define properly) that is futile to try to compensate.
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@lu_sichu @marclebel @davidbessis @Mlambm … On the other hand, ✺if✺ you manage to find an IQ measure that turns out to give the same average to sociologically diverse populations (NOT as a result of compensating), then you have some argument for claiming that you have one which isn't get biased by sociology.
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@lu_sichu @marclebel @davidbessis @Mlambm Because different populations mean ginormous sociological confounders which are always going to be impossible to cancel. A bit like trying to compare the weight of two different feathers each carried in a truck by taking the total mass and subtracting that of the truck. …
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@HalvorLande @lpachter @Mlambm @davidbessis I don't dispute the fact that there is correlation, I dispute the fact that the correlation tells us anything meaningful. It just tells us we're measuring the same (uninteresting) variable over and over, like “all maps just show population density”. x.com/gro_tsen/statu…
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@plumsirawit @Mlambm @davidbessis I think anyone who claims that normaliens are more intelligent than average is a fool. They are better at precisely what they have been selected for, and this is in no way a proxy for “intelligence”. But it is a (mediocre) proxy for the ability to do ✷some✷ math (or whatever).
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@marclebel @davidbessis @Mlambm No, I would say even less. If you find IQ differences between population groups, then pretty much by definition it tells you that your IQ measure is actually measuring a sociological phenomenon which isn't what you think.
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@IVANM31 @Mlambm @davidbessis Yes, this sounds far more reasonable.
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@srnorty @Mlambm @davidbessis It's just the equivalent of “every map just shows population density”. And the problem is that removing that trivial correlation to get to the phenomena you're actually trying to observe is essentially impossible (esp. if you don't know what they are).
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@srnorty @Mlambm @davidbessis This may be true, but it doesn't tell us anything useful: in sociology, every observable variable is highly correlated with every other variable, but the average axis defined by these correlations is just the trivial and uninteresting one (e.g., education, richness, etc.).
Now superimpose this map with one of where same-sex marriage is legal. 😂 x.com/OurWorldInData…
RT @OurWorldInData: Some parts of Europe have a growing population, while others are shrinking—␤␤The map shows which European countries saw…
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Or perhaps more bluntly: x.com/ArmyBarber/sta…
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As to what I think about IQ: x.com/gro_tsen/statu…
I attended the same school, and I can confirm this. Nobody was talking about their IQ. x.com/davidbessis/st…
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@Mlambm @davidbessis … is going to say a lot about the linear form used to project, and almost nothing about the phenomenon which we were trying to measure. In particular, mid-IQ people are just people in the “concentration of measure” bulk of the choice of linear form defining IQ.
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@Mlambm @davidbessis My objection as a mathematician (who attended the same ENS as the other David — and who also doesn't know their IQ) is that intellectual abilities are a very high-dimensional space, and that any attempt to project it down to a single number, viꝫ. linear form, …
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So everyone is making fun of that guy ⬇️ who made a shitty AI-generated video about what it would be like for the US to “free” Greenland (basically: open a strip mall with parking and huge 🇺🇸flags), but I guess, to him, Greenlanders are indeed severely lacking in freedom. 🤷 pic.x.com/XwTKXXLUhw
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To give just one example, Americans are often amazed by how many things are state regulated in Europe, but Europeans are just as amazed by the regulatory power of American municipalities and even homeowner associations. x.com/gro_tsen/statu…
Politics aside, the cultural differences between the United States and Europe in what people consider as “freedom” are absolutely fascinating to observe, so, yes, each side of the Atlantic will amaze that the other lacks freedom to do this-or-that. To much miscommunication. x.com/Daractenus/sta…
RT @Math_files: pic.x.com/FoapVIIWbe
RT @ngspiensfr: Si vous avez récemment fait blinder une porte et poser une serrure de sécurité et été satisfait du résultat, à Paris ou imm…
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And now the version with 5-fold symmetry instead of 7-fold symmetry (i.e., animating the still image quoted in previous post): pic.x.com/wEHMlhOQwe
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Mathematically the function plotted is ∑_i 2·cos(2π · (⟨p,v_i⟩ + t)) where p is the point in the plane, t is time, and v_i ranges over the vertices of the regular heptagon centered at the origin.␤␤Coloring as explained in this post: x.com/gro_tsen/statu…
(Mathematical art, I guess.)␤␤Phase-shifting the Fourier transform of a regular 14-gon. Or equivalently: seven plane waves meeting at equal angles. pic.x.com/1dEQxV6ygt
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Oh, here's an even nicer one: I plotted in white the region where the Fourier transform in question is between −1 and 1 (and in grayscale when it's between −1.5 and 1.5, black when it's above 1.5 in absolute value).␤␤Unexpectedly pretty! 🤩 pic.x.com/wjZaI5nJEv
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… and ⟨–,–⟩ is the Euclidean dot product.␤␤The left image shows the value on a gradient (blue = −10, black = 0, white = +10), the right image shows only the sign (black for <0, white for >0)
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To be clear, “Fourier transform of a regular decagon” means the Fourier transform of the sum of 10 Dirac measures, one on each vertex of the decagon.␤␤I.e. ∑_i cos(2π·⟨p,v_i⟩) where p is the point being considered, v_i ranges over all vertices of the decagon (centered at 0) …
Quasiperiodic (but not periodic!) image with 5-fold symmetry: the Fourier transform of a regular decagon. pic.x.com/rKtdiKD2No
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@JeanAbouSamra In particular, it settles this 🔽 particular case: if you have access to an omniscient but adversarial oracle who answers “yes” or “no” by giving you two Turing machines of which resp. 1 or 0-or-2 halt, you cannot use it to computably answer a question. x.com/gro_tsen/statu…
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Update: I got a very nice answer from @JeanAbouSamra who showed, by a smart 4-way restriction on Merlin's moves making the game effectively finite, that Arthur and Nimue have a winning strategy iff one can computably tell P×Q and Q×P apart. mathoverflow.net/q/503195/17064
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Pro-tip: si vous voulez éviter d'avoir l'air de hiérarchiser, il y a une astuce bien pratique employée à plein d'endroits: choisissez les intitulés, et classez-les par ordre ALPHABÉTIQUE.
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Non, sérieusement, personne ne s'est dit que ça envoyait un message… pas franchement terrible?␤␤Et je dis ça en tant que matheux, hein. xkcd.com/435/
Je ne veux pas dire, mais l'ordre dans lequel sont classés les sections du Comité national du CNRS cnrs.fr/comitenational… fait vraiment très «classification des sciences par positivisme décroissant selon Auguste Comte». 🫤 pic.x.com/24swqlf98S
Je ne veux pas dire, mais l'ordre dans lequel sont classés les sections du Comité national du CNRS cnrs.fr/comitenational… fait vraiment très «classification des sciences par positivisme décroissant selon Auguste Comte». 🫤 pic.x.com/fRhhQ2kO2L
Remember the good old days, six years ago, when we only had a global pandemic to worry about, rather than… <incoherent terrified gesturing>… all that shit?
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@ngspiensfr @JacqBens @laurentbercot … (I will admit, however, that the fact that the limit is 300 chars on Bluesky and only 280 on Twitter, with a different way of counting chars, turns out to be super annoying when I want to write the same thread on both.)
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@ngspiensfr @JacqBens @laurentbercot … So even with the ability to write longer posts I wouldn't do it, because the limit forces me to break things into small units of thought that can then be quoted, and I really like that. …
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@ngspiensfr @JacqBens @laurentbercot For me, the most annoying thing about the long posts is that you can't quote-post a specific part of it to comment or reply. I think the QP was the killer feature of this site (which Bluesky was wise to copy, and Mastodon stupid not to). …
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@laurentbercot … for the blue badge of worship,␤␤and also␤␤⁃ make any kind of regulation seem like a farce by randomly interpreting it over-broadly or ridiculously narrowly, so as to make it super annoying and to turn electors against the very idea of regulating digital content.
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@laurentbercot I may be cutting myself with Hanlon's razor, but I think there are two intents at play:␤␤⁃ turn this place into Elon Musk's court of worshipers (his ego needs it, but it also lets him control public discourse), by making it more and more annoying to people who won't pay …
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@Jilcaesel Right, the primary source is ideal; but for the kind of quotes I was talking about, viꝫ. widely circulating quotes on the Internet, the primary source is almost never what you will find by just googling the text of the quote.
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@nb4ld L'hébergeur est Scaleway (c'est une Dedibox).␤␤J'ai une IPv4 «failover» que je peux utiliser, au moins pour tester. (Mais chaque test est long et compliqué à mener.) Mais ça n'expliquerait pas vraiment que le problème se pose aussi en IPv6.
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A short video about the painting ‘Pandemonium’ by John Martin, and its inspiration: youtube.com/watch?v=k8kjPx…
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And yes, it can be infuriating how all the best quotes turn out to be apocryphal, and yes, it can be tempting to pass them on without verification, and think that it's just fun so no harm done.␤␤But I still think there is virtue in caring about proper sourcing.␤␤•4/4 pic.x.com/ata6UfgKvs
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In any case, a basic rule is: never trust a quote if there's just an author without context (book title, chapter & verse, date of speech…).␤␤If you're not sure, be honest: say “sometimes attributed to X”. You can also write “mistakenly attributed to X” or “common saying”.␤␤•3/4 pic.x.com/Clr0ZcipTg
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Wikiquote is generally reliable. Not 100%, but it's still MUCH better than sites with names like “brainy quotes” or whatever.␤␤Quote Investigator is super reliable, and will often tell you that the quote has been altered and (mis)attributed to N different people.␤␤•2/4 pic.x.com/exBLNMwzdC
👉 PSA: before attributing a quote to someone, especially if you found it on the Internets, if you still care about truth in this post-truth world, there are at least 2 places you should look: Wikiquote and Quote Investigator. Essentially all other sources are worthless. ⤵️ •1/4
La courbe des bouchons en Île-de-France est assez amusante pour aujourd'hui aussi: pic.x.com/Qu5xCJyvPs
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@JovianDesmond It is completely true that Venezuela is a narco-state (and, as I pointed out in reason #1, that Maduro is a horrible dictator). But this is still a “pretext” in that it is absolutely not the reason why Trump cares (except as a flimsy legal justification).
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…␤␤‣ Reason #4: Trump is jealous of how Maduro dances in front of a crowd, and he wanted to put a stop to that.␤␤bbc.com/news/videos/c1…
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… and went on press conference and blurted the quiet part out loud:␤␤‣ Reason #3: The US wants to seize Venezuela's oil.␤␤But to ✳︎really✳︎ understand what is happening we must dig deeper to the mysterious fourth level where the truth finally unfolds: …
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… to claim this one as a pretext. (Does he understand “authoritarian dictator bad”? 🤔) Next:␤␤‣ Reason #2: Mumble mumble drugs something traffic mumble narco gangs mumble.␤␤So this is the legal pretext under which they indicted him.␤␤Except that Trump didn't get the memo …
The 4 layers of reasons why the US abducted Maduro:␤␤‣ Reason #1: Maduro is (well, was) a brutal dictator, running a repressive régime in Venezuela.␤␤Just kidding. The above is perfectly true and might even have made for a semi-decent excuse, but Trump didn't bother trying …
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@nb4ld Oui, le DNS est tout en règle. Pour le blacklisting, c'est compliqué, parce que j'ai IPv4 et IPv6, mon IPv4 est blacklistée par SpamRats (et ça semble impossible à faire corriger) mais l'IPv6 non, et pourtant l'effet est exactement le même avec les deux.
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… So somehow the meaning was — uh, “averaged”, that is, damaged in transit — from “losing an eye” to “average”.
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… from the Arabic “ʿawāriyyaẗ” (“⁧عَوَارِيَّة⁩”, meaning “damage in transit”), relative of “ʿawār” (“⁧عَوَار⁩”, meaning “fault”, “defect”), from the root “ʿ-w-r” (“⁧ع-و-ر⁩”) meaning something like “to lose an eye”.␤␤…
This etymology is wild!␤␤#TIL The English word “average”, originally “custom duty” or “loss in transported goods”, comes from the French “avarie” (meaning “damage to a ship or cargo”) from the Italian “avaria” (same meaning), …
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The second, by Spencer (deputy district attorney, and incidentally former US marine) of the LegalEagle channel, tries to analyse the legality of the operation in US law, and whether the “it's an arrest, not an act of war” argument can work: youtube.com/watch?v=FCwdOe…
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The first is by William Spaniel, who specializes in the applications of game theory to geopolitics/geostrategy, and tries to make sense of what the US's strategy is. youtube.com/watch?v=HK91cD…
Two complementary videos which I found quite interesting, shedding light on the recent abduction of Nicolás Maduro by the United States: ⤵️
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Un candidat sérieux a été proposé sur l'autre réseau: Nicolas Hentz fr.wikipedia.org/wiki/Nicolas%5…
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… donc:␤␤👉 QUESTION: Qui est ce révolutionnaire français devenu riche propriétaire qu'aurait rencontré Tocqueville en Pennsylvanie?␤␤(Un candidat possible est Joseph Lakanal, mais d'après Wikipédia il était en Alabama, pas Pennsylvanie.)
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… (c'est-à-dire pendant la Révolution française) avait été «un grand niveleur» et «un ardent démagogue» dont le nom «était resté dans l'histoire», et il est frappé par le changement d'opinion politique de cet homme maintenant devenu riche.␤␤…
Je transmets la question d'histoire pointue suivante: ⬇️␤␤Dans “De la démocratie en amérique” (tome 2, ch. IX), Alexis de Tocqueville dit avoir rencontré dans «un des districts les plus reculés de la Pennsylvanie» un Français, devenu riche planteur, qui 40 ans auparavant … pic.x.com/mxxh58v5MG
Basically all outgoing mail I send (from my personal email server) is automatically classified as spam by many recipients including, and this is a huge problem, GMail.␤␤There is absolutely no explanation, no debug, no log, nothing.␤␤And yes, I have valid SPF, DKIM and DMARC.
#TIL the distinction between “to kidnap” and “to abduct”, at least from a (certain) legal perspective. x.com/Alonso_GD/stat…
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…␤“The person presenting the ultimate cachinnation possesses thereby the optimal cachinnation.” (=“He who laughs last, laughs best.”)
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…␤“When there are visible vapors having the prevenience in ignited carbonaceous materials, there is conflagration.” (=“There's no smoke without fire.”)␤␤“The writing implement is more potent than the claymore.” (=“The pen is mightier than the sword.”)␤…
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…␤“Eleemosynary deeds have their initial incidence intramurally.” (=“Charity begins at home.”)␤␤“Individuals who make their abode in vitreous edifices would be well advised to refrain from catapulting projectiles.” (=“People who live in glass houses shouldn't throw spears.”)␤…
“All articles that coruscate with resplendence are not truly auriferous.” (=“All that glitters is not gold.”)␤␤“Sorting on the part of mendicants must be interdicted.” (=“Beggars can't be choosers.”)␤…
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D'ailleurs, en fait, la carpocalypse (certes un peu retombée au moment où j'écris) a surtout l'air de concerner la Brie où, de toute façon, on peut toujours se brosser pour trouver des transports en commun. pic.x.com/RckuFnvtAy
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…␤␤⁃ et métro 6 tout cassé aussi, pour une raison qui n'a apparemment rien à voir, mais le métro trouve toujours une raison différente d'être malade;␤␤⁃ et à propos, à Paris, les trottoirs n'ont même pas été salés, donc même Rentre Avec Tes Pieds c'est bof. 🙄
Alors pour les gens qui essaient de profiter de la carpocalypse due à trois flocons de neige en Île-de-France pour faire la pub des transports en commun, je signale que je suis rentré en t.e.c. et que:␤␤⁃ plus aucun bus,␤␤⁃ qqch comme 1 RER B sur 3, qui va à mi-vitesse,␤␤…
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@Jilcaesel … The current idea, IIUC, is that this is admissible under a UN Security Council resolution. But as you certainly know, these are… kind of hard to get agreement on, even for something as minimal as sanctions.
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@Jilcaesel Not at all. Many political philosophers have tried to theorize the right to intervene in a foreign country to defend human rights (so, a limit to Westphalien sovereignty). But of course there is little agreement on the details. …
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And of course, in a region where it very rarely snows more than a few millimeters, when it does snow more than that, everything is thrown into chaos because there is no infrastructure to deal with it. pic.x.com/raXSRkP1rT
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We typically have maybe 1 day of snow per year here, but of course it had to be the one day where I really needed to come to the office. pic.x.com/0yPA45SkDH
This image posted on a colleague's door made me laugh. pic.x.com/3gMPznDtsA
Frost-covered trees¹ in Palaiseau / Triffouilly-lès-Saclay. 🥶␤␤1. They seem to have finite branching and finite branches, but I'm not sure I can deduce that they are finite trees. pic.x.com/niTSs7qweP
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La gare routière de Massy-Palaiseau, c'est vraiment spectaculaire: tous les bus vont et viennent complètement vides, sauf celui pour Triffouilly-lès-Saclay qui est bondé à toute heure du jour et de la nuit.
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Résultat, 20min d'attente immobile dans le froid (et le bus, par contre, est surchauffé).
C'est qui le gros naïf qui s'est dit que par un temps froid pareil ce serait quand même moins déplaisant de prendre le bus depuis Massy-Palaiseau jusqu'à Triffouilly-lès-Saclay plutôt que de monter les escaliers verglacés du Guichet? C'est Bibi!
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@Jilcaesel Celle-là n'est pas la plus intéressante, mais les 2min où il fait ce point sont assez rigolotes (je trouve).
RT @vtchakarova: After carefully monitoring the situation in Venezuela for the last 24 hours, the EU has found out that the water bottle of…
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@Jilcaesel Tiens, puisque j'ai vu que tu as fait ce point plusieurs fois, ça t'intéressera peut-être que William Spaniel (spécialiste de théorie des jeux appliquée à la géopolitique) le souligne aussi, avec un sarcasme assez amusant, dans la vidéo youtube.com/watch?v=e4SVt3… [7′42″–9′24″].
What was the geopolitical context referenced by the “fabricated drug war” in this comic? US support for the Nicaraguan Contras? x.com/metasynthie1/s…
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@laurentbercot @Jilcaesel … Il serait d'ailleurs intéressant de voir les arguments juridiques invoqués par les avocats d'Eichmann sur la question du mode d'arrestation (pour la compétence je suppose que c'était sous la compétence universelle pour crimes contre l'Humanité).
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@laurentbercot @Jilcaesel … même si évidemment les avocats de Maduro vont arguër des circonstances, disons, inhabituelles, de son arrestations, et probablement du Foreign Sovereign Immunities Act de 1976, mais disons que la question n'est pas aussi évidente que je le prétendais. …
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@laurentbercot @Jilcaesel @KyleKulinski … Or je parlais là de la question de l'inculpation de Maduro en droit américain interne, pas de la question de l'illégalité de l'intervention en droit internationale (qui est évidente) ou américain (qui est plausible). Ce sont des questions juridiques bien différentes, …
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@laurentbercot @Jilcaesel @KyleKulinski Oui mais c'est une question différente: @Jilcaesel me faisait remarquer que j'étais un peu trop péremptoire en déclarant que, du point de vue strictement juridique, les cours de justice américaine n'ont pas jurisdiction sur le Venezuela. …
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But if US judges actually decide to uphold the rule of Law and vacate the charges, I am curious to know what the US Administration will do next. Send him back to Venezuela when they have taken power there so he can be judged by a kangaroo court?
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According to bbc.com/news/articles/… the main charge is “conspiracy to commit narco-terrorism and import cocaine [into the United States]”.␤␤Under the normal rule of Law, of course, US courts have no jurisdiction over Venezuela, but we do not live in normal times. 🤷 pic.x.com/v2Cpq26RBT
OK, but seriously-seriously, it's going to be extremely interesting¹ to watch what the US actually charges Maduro with, before which court, and how it unfolds.␤␤(I understand they're not just “disappearing” him in Guantánamo.)␤␤1. As in: “may you live in interesting times!”. x.com/gro_tsen/statu…
RT @ggooooddddoogg: achieving AGI by reducing the intelligence of the average human rather than increasing the intelligence of AI
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[Link to aforequoted post: bsky.app/profile/gro-ts… ]
Now is just as good a time as any to point out that the name of the Saudi royal family is “ʾĀl Suʿūd” (“⁧آل سُعُود⁩”), wherein “ʾĀl” (“⁧آل⁩”) is not the definite article but an actual noun meaning “family”.␤␤In particular, it should be capitalized in English. pic.x.com/V7UVIOfsRp
I think the BBC meant to say that the correct answer to the titular question below is “we have no f🤔cking clue!”. bbc.com/news/articles/… pic.x.com/k4fr6Zv82U
Seriously, though: are they going to charge Nicolás Maduro with entering the US illegally without a visa?
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@Jilcaesel ‼️ chef d'état autoritaire et corrompu sans respect pour l'état de droit fait enlever chef d'état autoritaire et corrompu sans respect pour l'état de droit
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@Jilcaesel Also in the news:␤␤⁉️ chef d'état autoritaire et corrompu sans respect pour l'état de droit fait enlever chef d'état vaguement démocratique␤␤⁉️ chef d'état vaguement démocratique fait enlever chef d'état autoritaire et corrompu sans respect pour l'état de droit␤␤Mais en fait:
RT @OPTester_Chris: This is meme is so relevant right now it hurts. pic.x.com/YFj1M68tQO
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‣ Update: more radical leftist talk from the same person in 2019. x.com/TulsiGabbard/s… (= archive.is/f0Pb1 ) I really wonder what became of her in 2026? pic.x.com/BQAN17Vi3G
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reddit.com/r/math/comment…
Interesting question asked (implicitly) on Reddit /r/math: does there exist a closed term V of the (pure untyped) λ-calculus such that (f ((V f) (f x))) reduces to f x (in other words, V f computes a partial inverse of f; this is easy to do in the 1st Kleene algebra)?
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(Sincere apologies to Dante.)
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“Nel midjourney di nostra vita␤mi ritrovai per un' AI slop oscura,␤ché la retta immagine era smarrita.”
“In the midjourney of our life␤I found myself in a dark AI slop,␤for the right image was lost.”␤␤😄 pic.x.com/WCELB1AA7o
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@Jilcaesel 🤣
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@Jilcaesel Next thing you're going to tell me you wouldn't immediately see a ram in the first image if you don't have the help from the second image! 😉 pic.x.com/aSNTtSBafL
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… so it's certainly not like the Southern Cross was entirely unknown in the West before Magellan and Da Gama. But whether Dante had access to this information isn't something I can decide. I don't know if historians have settled this question. •22/22 pic.x.com/nieA44RBKg
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Even earlier in time, around the time of Claudius Ptolemy (2d century astronomer), Acrux was at −53° declination, so the Southern Cross was clearly visible even in Alexandria, and IIUC, Ptolemy did catalogue these four stars in his ‘Almagest’ (as part of the Centaur), … •21/22
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… Acrux was only at −59° declination, so it would have been (barely!) visible from Cairo (which is at a latitude of 30°N) looking south in winter. The Crusaders might have seen it and talked about it (seeing a bright cross in the sky probably would have struck them!). •20/22
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Right now, the southernmost star of the Southern Cross (Acrux) has a declination of −63°, making it (and hence the entire cross) visible above the horizon only up to a latitude of 27° north. But in Dante's time, because of precession of the equinoxes, … •19/22
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It does look a lot like Dante is goading us with a mystery: “nobody has seen these four stars since Adam and Eve, and yet somehow I know about them! how is that possible?” — so it is conceivable that it was deliberate. Might Dante have know about these stars? •18/22
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(But then he does write “le quattro luci sante” — “the four holy lights” — a few lines down, so maybe this is referring to the shape of a cross after all? I have no idea.) •17/22
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In favor of the imagination hypothesis is the fact that he doesn't describe the stars as having the shape of a cross, which is certainly something he would have wanted to do given how it would beautifully tie in with the Easter symbolism. •16/22
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So, did Dante know about this? Could he hypothetically have known about the Southern Cross? It is entirely plausible that he was inventing or speaking metaphorically (after all, the ‘Divine Comedy’ isn't exactly hyperrealistic). •15/22
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So Dante is saying “I turned toward the right [i.e., toward the south, because he had been looking east toward Venus rising] and saw four stars never seen by anyone except for Adam and Eve”. This is fairly striking when the pattern here is indeed the Southern Cross! •14/22
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… “I' mi volsi a man destra, e puosi mente / a l'altro polo, e vidi quattro stelle / non viste mai fuor ch'a la prima gente.” — “I turned toward the right, and thought / of the other pole [= South pole], and saw four stars / not seen before except by the first people.” •13/22
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… at that point in time (per Stellarium), Venus was below the horizon, it would only rise after the sun. Dante should be seeing Mars. But it is correct that the constellation Pisces (the Fish) would be rising in the east. ❧ But now look at what Dante says next: … •12/22
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… please apologize my clumsy translation of 14th-century Italian coming from a French speaker with only rudimentary knowledge of Italian 😅): this is clearly saying that Venus was visible in the East, and this is wrong: … •11/22
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… for example, he writes “Lo bel pianeto che d'amar conforta / faceva tutto rider l'orïente, / velando i Pesci ch'erano in sua scorta.” (“The beautiful planet which incites love / makes all the orient laugh / veiling the Fish that were in its train” — … •10/22
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So we can assume Dante payed particular care to the description of the sky that is the very first thing he does in the first canto of ‘Purgatory’ (the second part of the poem). Now of course 14th-century knowledge of astronomy wasn't perfect (that's an understatement!): … •9/22
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Now stars play a very prominent role in Dante's work: the very last word of each part of the ‘Divine Comedy’ is “stelle” (stars); the last verse in ‘Hell’ is: “E quindi uscimmo a riveder le stelle.” (“And thence we emerged to see the stars again.”) •8/22
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Four stars clearly visible near the south-southwestern horizon are Acrux, Becrux (also known as Mimosa), Gacrux (not labled by Stellarium, but down from Mimosa) and Decrux (also known as Imai, dimmer, completing the cross), with magnitudes 1.25, 1.25, 1.55 and 2.75. •7/22
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… and this is what the astronomy program Stellarium shows me as the sky which Dante and Virgil should have seen, looking toward the south-southwest, on the morning of April 10, 1300, at the antipodes of Jerusalem: ⬇️ •6/22 pic.x.com/cCvYnYJGiT
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… and they emerge at dawn, and we are also told by Virgil that the antipodes are 12 hours behind Jerusalem (apparently Dante had decided where the international date line must lie 😆). So, around Julian Date 2195983.145 or so, at latitude 31.78°S and longitude 144.76°W … •5/22
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In fact, the emergence of Dante and Virgil is amazingly well situated in both time and place: not only are they at the antipodes of Jerusalem, but the date is very precisely set: it is the morning of Easter Sunday (which would be April 10) of the year 1300, … •4/22
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… at the antipodes of Jerusalem (which in real life would be here: openstreetmap.org/?mlat=-31.7780… — not much to see) lies the mountain of purgatory, which, per Dante, is the only feature of the southern hemisphere (the rest has been covered by water). •3/22
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Here's the setup: at the end of ‘Hell’ (the first part of Dante's ‘Divine Comedy’), Dante and Virgil make their way out of the inverted funnel of hell, through a hidden passage (“cammino ascoso”) connecting the center of Earth (the tip of the funnel), to the antipodes: … •2/22
Oh, speaking of star patterns, here's a more interesting question, with ties to history:␤␤‣ Did Dante Alighieri, circa 1320, know of the Southern Cross?␤␤(The Southern Cross is a prominent group of 4 bright stars in the southern hemisphere, in the shape of a cross.)␤␤🧵⤵️ •1/22 x.com/gro_tsen/statu…
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@laurentbercot (Which probably says a lot about the way our brains keep judgments “in cache” and how difficult it is to force ourselves to re-evaluate these judgments.)
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@laurentbercot And the funny thing is that, for me at least, even after I wake up, I continue to think that the epiphany is perfectly sensible (and sometimes I want to tell others about it 😅), it's only when I force myself to reconsider it that I realize it's pretty nonsensical.
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… But still, the basic question of whether people with no knowledge of astronomy can subconsciously tell a real star field image from a fake-but-plausible one might be mildly interesting to test.
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… which makes no sense at all. (I think there was a kind of detective story and I thought I was smart by proposing to test a suspect's story with this experiment.) Or maybe it was about showing them the stars at the moment of their birth, which would make even less sense. …
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… The dream, of course, was confusing and incoherent, as dreams tend to be, and then the plot involved how one could tell whether someone was present at a particular time and place by showing them the night sky for that particular time and place and measuring their reaction, …
Last night I dreamt that, according to a famous psychology experiment, if you show people (even with no knowledge of astronomy, I guess!) an image of a night sky, their brain reacts differently than if they are shown a random fake / imaginary — but plausible — star field. …
RT @GeorgesBerger: Bonne année pic.x.com/Oyb1ELLYFT
I ordered delivery of a new me for today, but I didn't receive anything: where am I supposed to complain?
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@Jilcaesel Oui, je ne nie pas que les différents moyens de limiter longueur des lignes ont tous des inconvénients, mais il y en a plus, et leurs inconvénients sont moins graves, que l'opération contraire, donc je privilégie naturellement ce qui est le plus faisable.
Just in case anyone thought buffer overflows and insecure C code were a recent phenomenon, there is a buffer overflow in the code of the “su” program from Unix v4 (circa 1973, probably written by Ken Thompson): sigma-star.at/blog/2025/12/u…
Fiona Ross, “A thread in the labyrinth”, 2011 (6″×6″, micron ink on Denril paper)␤␤A piece of art consisting of a single Jordan curve.␤␤Included in the paper “The Jordan curve theorem is non-trivial” by Fiona Ross & William T. Ross (‘Journal of Mathematics and the Arts’, 2011) pic.x.com/5aJny0vskB
The community note on that one is a thing of beauty. [Tweet id: #1877501353175478525] pic.x.com/K4aRuDO2hg
RT @philosophymeme0: pic.x.com/rIldtmC45Z
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@Jilcaesel ‼️ rebelles sanguinaires s'opposant au gouvernement sanguinaire du Yémen␤␤(mais je suis d'accord sur le principe de résumer au moins globalement le contexte)
RT @philosophymeme0: pic.x.com/1BP1ugpi1V
RT @messedupcars: pic.x.com/tkmrpsaOck
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C'est une version plus développée de ce fil: x.com/gro_tsen/statu… x.com/gro_tsen/statu…
Un petit rant sur mon blog pour finir l'année, concernant l'impossibilité pour l'utilisateur de configurer le style des pages Web: madore.org/~david/weblog/…
Another way of describing this diagram is that it shows which numbers of the form 3^x · 5^y are close to a power of 2.␤␤(Where y is read vertically from the central line, and x is read horizontally from the obvious northeast-southwest line through the center.) x.com/gro_tsen/statu…
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Anyway, for better explanations about this, I refer to JCB's blog post here: johncarlosbaez.wordpress.com/2023/11/06/jus… (can you spot how his basic parallelogram appears as an approximate period in my diagram?). •19/19
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An important one in music is that 3 just fifths plus 1 minor third, so, 3 steps east and 1 step southeast in my diagram gives (2 octaves plus) a small interval with frequency ratio of 81/80 (that's 21.5 cents) that often gets smeared away when constructing musical scales. •18/19
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For the same reason that log(2), log(3) and log(5) are linearly independent over the rationals, the diagram is never exactly periodic, but there are arbitrarily good approximations, so arbitrarily good “almost periods”. •17/19
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For example, 12 hexagons to the east of the central one, we have a yellow hexagon (quality: 23.5 cents), because 12 perfect fifths gives almost 7 octaves. But 12 hexagons east of that is only reddish (quality: 46.9 cents) because 24 fifths isn't so close to 14 octaves. •16/19
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Because when you have an approximate match (i.e., some combination of fifths and thirds that is nearly an integer number of octaves), by adding it again and again, the errors accumulate, and the quality of the match decreases. •15/19
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… except that the center hexagon has been made green instead so we can easily tell where it is (but in principle it should be pure blue). ❧ The thing about the diagram is that it LOOKS periodic, and it is APPROXIMATELY so, but not exactly! •14/19
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(Yes, this is a purely arbitrary color gradient, I didn't give it much thought. It's somewhat reminiscent of star colors.) Anyway, red-to-white are good matches, and white-to-blue are pretty much inaudible differences, with pure blue representing an exact match, … •13/19
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… intervals between 50 and 25 cents are colored red-to-yellow (with bright yellow for 25 cents), intervals between 25 and 12.5 cents are colored yellow-to-white (with pure white for 12.5 cents), and below 12.5 cents we move to blue. •12/19
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Black hexagons are those which distant from the reference note by more than 1 halftone (where here, “halftone” refers to exactly 1/12 of an octave in log scale), or 100 cents. Intervals between 100 and 50 cents are colored red (bright red for 50 cents), … •11/19
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Since log(2), log(3) and log(5) are linearly independent over the rationals (an easy consequence of uniqueness of prime factorization!), NO two notes in the diagram are exactly equal. But they can come very close! And this is what my colors show. •10/19
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Mathematically, if we talk about the log base 2 of frequencies, modulo 1, we can say that one step to the east adds log₂(3), and one step to the northeast adds log₂(5) (all values being taken modulo 1). •9/19
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The entire grid is known as a “Tonnetz”, as explained in Wikipedia en.wikipedia.org/wiki/Tonnetz — except that unfortunately my convention (and JCB's) is up-down-symmetric wrt the one used in the Wikipedia illustration. 🤷 •8/19
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And the hexagon to the southeast of any given hexagon is one minor third above (frequency ×6/5) or equivalently, one major sixth below (×3/5); and the one to the northwest is one major sixth above (×5/3) or one minor third below (×5/6). •7/19
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The hexagon to the northeast of any given hexagon is one major third above (frequency ×5/4) or equivalently, one minor sixth below (frequency ×5/8). Symmetrically, the hexagon to the southwest is one minor sixth above (×8/5) or one major third below (×4/5). •6/19
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And of course, symmetrically, the hexagon to the west (i.e., to the left) is precisely one just fourth above, i.e., 4/3 the frequency, or equivalently, one just fifth below (2/3 the frequency). •5/19
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More precisely: for each hexagon, the one to its east (i.e., to its right) is the note precisely one just fifth above, i.e. with 3/2 the same frequency; equivalently, it is the note one just fourth below (i.e., with 3/4 the frequency) since we are talking modulo octaves. •4/19
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… in the sense that two notes separated by an integer number of octaves are considered the same note. And when two hexagons are separated in the same way in the diagram, the notes are separated by the same interval (modulo octaves). •3/19
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So, each hexagon in my diagram represents a musical note, or frequency, relative to a reference note which is the bright green hexagon in the exact center. Actually, more precisely, each hexagon represents a note modulo octaves … •2/19
This almost-but-not-quite-periodic image is inspired by a recent blog post by John Carlos Baez about musical scales: let me explain what I drew here, and what it has to do with music, but also with diophantine approximations of log(2), log(3) and log(5). 🧵⤵️ •1/19 pic.x.com/wCufyMAe3j
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@ngspiensfr @laurentbercot Oh wait, I published on September 11 a program where you have to CATCH FALLING THINGS? That's certainly suspicious, isn't it!
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@ngspiensfr @laurentbercot Here it was: pic.x.com/utpDaUc5Lq
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@ngspiensfr @laurentbercot I remember filling such files for xletters and a few others, and uploading them… somewhere, I'm not quite sure where. And then there were search engines of sorts.
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@laurentbercot @ngspiensfr Also, do you remember when LSM files were a thing? en.wikipedia.org/wiki/Linux_Sof…
Pas mal, mais j'aurais ajouté quelque part la devise: “Quoi d'autre?” x.com/laurentbercot/…
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@kebabroyal_ Ah non, maintenant il faut dire «quoi d'autre?». 🧐
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I feel he's not nearly arrogant enough. He'll never properly assimilate.
George Clooney just got French citizenship‽ What‽
RT @DeathMetalV: Gayer than gay porn x.com/iAnonPatriot/s…
Je prends un brunch alors qu'on n'est pas dimanche et j'ai l'impression d'être un gamin qui fait un truc interdit.
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(There are 3 kinds of mathematicians: those who can count and those who can't.)
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Whatever the case, Weyl has anteriority, so you can go ahead calling 57 the “Weyl prime” instead of the “Grothendieck prime”.
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My phrasing is confusing. Weyl unquestionably made the mistake of calling 57 prime. But somehow the story is about Grothendieck. It could be that G. made the same mistake independently. Or it could be that the story about W. was mistakenly told about Grothendieck.
According to this MathOverflow post, the famous story about the “Grothendieck prime” 57 (viꝫ. that Grothendieck may have once used this non-prime as an example of a prime) may actually be about Hermann Weyl (or Weyl made the same mistake). mathoverflow.net/q/326912/17064
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@laurentbercot (CSS flex both tries to make layout less confusing, and does empower the user to some extent because it allows for a wide range of widths and sizes, not just the one or two that the site author coded for. It's not perfect, but it's still worth saving.)
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@laurentbercot I don't entirely agree. I think this is the result of an accumulation of excessive and badly thought-out complexity. Some bad will, but mostly just lack of any forethought. Still, some CSS standards, like flex, are actually good and try to make things less awful.
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@laurentbercot This might make sense because of forward-compatibility (a Web site author was allowed to assume default colors were black-on-white so might add an explicit black color on text somewhere, which would make it unreadable in “dark mode”). But I agree everything sucks about this.
RT @ngspiensfr: I needed a tool to make a few Unicode transformations on a small text, so I wrote one.␤nsup.org/phare/gitweb?p… https://t.co…
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… but this is so infuriating! It is not up to ME to choose your line length for YOU. Eventually I hacked a bit of JS magic to let users change it, but it's hacky and brittle and requires local storage, and it's not easily discoverable. Why does it have to be this way? 😡 •7/7
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On my own site, I like to avoid needlessly setting CSS values if I don't know user preferences. So, e.g., text lines span the entire width of the window (I assume users who want shorter line lengths will resize their window), per default. Many users complain about this … •6/7
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(Oh wait, they did eventually come up with one common preference: it's called “light” or “dark” mode: developer.mozilla.org/en-US/docs/Web… — that's it, ONLY ONE BIT. Of a gazillion things the user might want to choose, only THIS ONE BIT is allowed to filter through.) •5/7
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Why should I, a content creator, decide for you what font and size you should read my content in, what colors, what line length, that sort of things? I don't care: you're the one doing the reading! You should be in charge of choosing such things. •4/7
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There is simply NO way to get user preferences. You CAN make your Web site customizable, but you have to design a customization UI from the ground up. There is no way for users to give their browser “standard basic preferences” that would be followed everywhere by default. •3/7
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I understand that Web sites might want to do a bit of branding, but it makes far more sense for USERS to set their OWN preferences on how Web pages to look like (fonts, colors, character sizes, etc.) which should be followed by default. •2/7
Here's the absurd thing about Web page styles: every site defines their own look&feel for ALL users, and there is no standardized way to allow users to express preferences. This is completely crazy and backwards. 🧵⤵️ •1/7
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In fact, I like Meteoblue's meteogram so much that I have a dedicated LCD screen in my living room (connected to a NanoPi) that alternates between that and their 10-day forecast, so I can tell the weather at a glance. pic.x.com/ny8b3neHvV
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@ngspiensfr Je dirais que le ‘ω’ ne devrait pas avoir de serifs aux extrémités supérieures gauche et droite. D'abord parce que canoniquement il n'y en a pas, et ensuite parce que ça ressemble trop à ‘w’.
Everything is great about this chart: instead of just a daily minimum and maximum we get an actual temperature curve; besides the pictograms we get a cloud density profile, precipitations are also shown by time of day (here there are none), and even the wind graph is useful! x.com/gro_tsen/statu…
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@econchon Actually, I think Meteoblue's killer chart is their “meteogram”: meteoblue.com/en/weather/for… — this shows everything I want to see about the weather in a nice graphical layout. I've never seen anything like that anywhere else and I wish other sites would imitate it. pic.x.com/QzsMzLgLpK
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They try to explain what “predictability” means on content.meteoblue.com/en/specificati… — but I'm not sure I understand the explanation.␤␤In practice, x% predictability probably means x% of simulation runs fall in some window of parameter tolerance, but the window isn't clearly specified.
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Chart taken from here: meteoblue.com/en/weather/10-… (I recommend this site, at least for weather in the EU: they seem to understand how to make clear charts when no one else does).
I like the fact that this weather site is very honestly telling me “I have 0% confidence in the weather I am showing for 2026-01-08 and 2026-01-09” 😁 pic.x.com/QHWYhtiHkL
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doi.org/10.1016/S0022-…
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(Le truc, surtout, c'est que si je choisis ⓑ, il y a 1 chance sur 2 pour que mon cerveau me réveille à 4h du mat' en ayant décidé qu'il était ABSOLUMENT INDISPENSABLE de comprendre TOUT DE SUITE pourquoi le topos de la réalisabilité modifiée ne valide pas le principe de Markov.)
Dimanche soir, une tasse de thé à la main, confortablement installé: est-ce que je vais␤␤ⓐ essayer de comprendre pourquoi le topos de la réalisabilité modifiée ne valide pas le principe de Markov,␤␤ou bien␤␤ⓑ lire une BD?␤␤Difficile est le choix!
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@kabeljauherrman Not true! Besides the US president and the US president's son, there are many different people in the US president's entourage and administration that this could be referring to.
RT @NoContextBrits: pic.x.com/r5K4Z0RNXp
The whole thing sounds more like the setup for a joke (“the head of the Taliban, secretary of the CCP and Greta Thunberg enter a bar…”) or of a subtle logical puzzle where each door has a guardian who either always lies or always tells the truth or randomly spouts propaganda. 😏 x.com/gro_tsen/statu…
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Note that Peter Thiel has been spouting this particular “three doors” nonsense for some time now, because I already discussed this here on Twitter before: x.com/gro_tsen/statu…
Ignoring the irony that the guy behind Palantir is warning us about surveillance, it's also telling that Peter Thiel thinks three equally dystopian futures are: Islamic Šarīʿaẗ law, being ruled by the Chinese Communist Party, and… riding a bicycle with Greta Thunberg. 🤣 x.com/panickssery/st…
#TIL Woody Guthrie wrote a song about how racist Trump was, back in 1954 (“I suppose / Old Man Trump knows / Just how much / Racial Hate / He stirred up”) en.wikipedia.org/wiki/Old_Man_T…␤␤Yes, of course, this is about Fred Trump, the father of the current US President.
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The only explanation I can imagine is this: YouTube must think every translation of a video is a different video for audience targeting purposes, and since it must have categorized me in the “watches videos in language X” group for X in {en, fr, de}, I get this.␤␤Still stupid!
This is happening more and more frequently: YouTube is randomly, and not even consistently, showing me French translations of videos that are originally in English AND ALSO English translations of videos that are originally in French.␤␤What the actual f🤯ck? WHY? x.com/gro_tsen/statu…
RT @CSMFHT: Wow spoilers lol pic.x.com/wGldp3fhJ8
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@GenevieveMadore x.com/gro_tsen/statu…
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An analysis of the rise, decline, and rise again, of Internet piracy⌫file sharing — how the convenience of Netflix had made it gone away, and how the fragmentation of streaming platforms brought it back: youtube.com/watch?v=kvkWkN…
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Bon oui en fait, Paris c'est pas si mal. Froid, beau et sec c'est toujours mieux que froid, moche, venteux et neigeux. pic.x.com/aeMb9u57ai
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Le côté canadien de ma famille rigole et trouve sans doute que je dois rendre ma nationalité. pic.x.com/zmXdwVkJT7
Moi, chaque été: «La chaleur, c'est vraiment pénible. Le froid c'est quand même plus supportable, parce qu'il suffit de se couvrir.»␤␤Aussi moi, chaque hiver: 🔽 x.com/gro_tsen/statu…
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Et voici enfin la partie 4, consacrée à divers sujets en lien avec les réels: madore.org/~david/weblog/…
RT @TerribleMaps: Africa is so big you could fit a smaller Africa within its borders pic.x.com/jgYg23LUMO
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@JeanDellass Je n'ai pas fait Polytechnique non plus, donc je ne peux pas juger! 😁
Observation du jour: les gants chauffants pour moto peuvent servir même quand on ne fait pas de moto.
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@JacqBens … surtout que je ne voulais pas, la veille de Noël et par temps froid, faire un long trajet à moto; mais évidemment, comme c'est dans Paris, c'est plus cher que ce qu'on trouverait sans doute ailleurs.
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@JacqBens Il faut quand même dire que je n'ai pas cherché le moins cher; les centres de contrôle technique sont privés, ils sont juste régulés par l'État mais pratiquent des prix de marché: il y en a un à 5min (à pied!) de chez moi, donc je suis allé là, …
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… Et ce qui est marrant, comme lui a fait remarquer mon poussinet, c'est que si au lieu de demander à ChatGPT une solution, elle avait demandé à ChatGPT de générer un programme en — disons — Prolog pour calculer une solution, ça aurait probablement été bon, pour le coup.)
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(OK, ce n'était pas complètement évident, comme problème, parce qu'il y avait pas mal de contraintes du style les enfants ne font pas de cadeaux aux parents ou vice versa. Mais justement, ChatGPT n'a pas été foutu de tenir compte de toutes les contraintes imposées. …
Je ne veux dénoncer personne, mais j'ai une cousine qui a beau avoir fait Polytechnique, pour générer une permutation cyclique «qui offre un cadeau à qui» sur 15 personnes à Noël, elle a fait appel à ChatGPT, et ChatGPT a, évidemment, fait de la merde. 🤣
RT @ProofreadJulia: pic.x.com/wYWQhetM3f
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@JacqBens … Comme souvent ce genre de mesures est un compromis merdique entre toutes sortes d'intentions partiellement contradictoires (dont, oui, taxer, et aussi contrôler toutes sortes de choses pas très cohérentes entre elles).
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@JacqBens … en tant que motard qui a gardé mon pot homologué et essaie de ne pas faire trop de bruit je suis plutôt favorable à cette idée générale, mais je trouve quand même que ~90€ pour essentiellement just vérifier mon pot d'échappement, c'est un peu cher payé. …
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@JacqBens S'agissant des motos spécifiquement, je pense qu'une des raisons de la mesure est de faire la guerre aux motards qui remplacent leur pot d'échappement d'origine (homologué) par un Akrapovič conçu (ou plutôt: modifiable) pour faire beaucoup plus de bruit: …
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@JacqBens C'est tous les 2 ans, sauf que pour les motos c'est tout nouveau donc il y a un déploiement progressif.
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‣ Update: here's some info on the tape's contents: spinellis.gr/blog/20251223/…
RT @SaarelaHC: Highland Cattle photo of the day pic.x.com/0tfWWmVSgi
Premier contrôle technique moto favorable! 🥳 pic.x.com/5fbaS20HzU
Useless info, but since people are talking about him: Thierry Breton is my cousin's husband. (Second cousin once removed, I think. And, no I've never met him.)
RT @gro_tsen: 🚨🎅 In this season it is important to know your 🇪🇺 GDPR rights!␤␤The following template letter might be of use, especially if…
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An explanation of China's “Social Credit” system and Western myths and misconceptions surrounding it: while something of the sort does exist, most ideas circulating around it in the West are misunderstandings, mistranslations or outright inventions. youtube.com/watch?v=iXrx9r…
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An 11-video playlist on the Standard Model of particle physics: youtube.com/watch?v=qtf6U3… (each one is pretty short).␤␤The level of prerequisites in the explanations varies a bit randomly, but I still think this does a superb job of explaining so many things in such a short time.
Mood: enough to eat, I don't care about the rest. x.com/SaarelaHC/stat…
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@JacqBens Well, liking constructive math is a bit of an oysters-or-snails situation: I wouldn't want to push my tastes onto anyone else. 😏
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@Jilcaesel It would be hard to make it fiction, but maybe I can make it not nonfiction. 🤔
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@Jilcaesel So none of my blog posts seem to go beyond the “novella” category. But all four published so far parts of my “constructive math” series total ~58k words.␤␤(First you tell me it's fiction, now you tell me it's a novel! Great, I'm on a good track, it seems.)
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@Jilcaesel So, what's the threshold value?
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Anyway, part 0, which includes a table of contents with links to the entire series so far, is here: madore.org/~david/weblog/…␤␤The very start (history & motivations) is supposed to be understandable even by non-mathematicians.
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… If you don't know at all what “constructive math” is, in short it refers to mathematics done without the Law of Excluded Middle.␤␤Why one would even want to do such a thing (which Hilbert called “boxing without one's fists”) is explained in part 0. 😁
Perhaps it's worth reposting in English:␤␤👉 I'm writing a series of (long) blog posts that form an introduction to constructive math, maybe to become a book eventually. They are in French, but I think Google Translate does a pretty good job these days on this kind of content. …
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@laurentbercot @Astatide42 @informatheux The Good Place isn't the Best Place. 😔␤␤(The Best Place is the friends you made along the way. 😁)
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Si vous n'avez pas suivi la série, je conseille de commencer par ce billet, que j'y ai rétroactivement intégré comme «partie 0», qui explique de quoi ça cause; le début (historique) est censé être compréhensible au grand public: madore.org/~david/weblog/…
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Logiquement je devrais continuer en parlant de topologie, puis de continuité, mais je crois que le format blog atteint ses limites et qu'il faut vraiment que je commence à transformer ça en un livre.
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Il y en a une partie 4 déjà écrite (parce que j'ai coupé en deux un truc vraiment trop interminable) et que je compte publier dans quelques jours. Ça parle de propriétés un peu plus intéressantes: suites de nombres réels, et principes analytiques d'omniscience.
J'ai enfin publié la partie 3 de ma série de longs billets sur les mathématiques constructives: madore.org/~david/weblog/…␤␤Ça parle de la définition des nombres réels et leurs propriétés de base, essentiellement en rapport avec l'ordre.
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@Jilcaesel @Astatide42 @informatheux At some point I tried doing this (using a list instead of home timeline) but the issue was that there was one specific poster for whom I wanted to see posts but not reposts, and IIRC lists don't allow that.␤␤(On the Good Place, it's the other way around: ONLY that is allowed. 🤷)
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… Aaaaaand it's back to “normal”. 🤷
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@fcqv This reply I got on the Good Place seems to be the best explanation: pic.x.com/yKI4HadQ6k
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@antoineducros @informatheux @ngspiensfr … et que tu ne veux probablement pas que l'instant de l'équinoxe ou du solstice dépende de ces petites oscillations, donc tu veux probablement prendre un axe moyen qui les supprime (ce n'est qu'un exemple de ce qui peut se produire, mais tu vois l'idée).
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@antoineducros @informatheux @ngspiensfr Non non non, je ne dis pas qu'elle n'est pas raisonnable, je dis juste qu'elle n'est probablement pas bonne si tu veux une précision de l'ordre de la minute ou mieux. Par exemple parce que l'axe instantané de rotation de la Terre a plein de petites oscillations, …
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@pbeyssac @ngspiensfr @informatheux … mais là dans la définition de «solstice», c'est la définition même qui pose problème pour la précision: qu'est-ce que c'est, exactement, le solstice? La position de la Terre ou du Soleil ou d'une étoile, ce sont des choses qui ont un sens réel, l'équateur et l'écliptique, non.
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@pbeyssac @ngspiensfr @informatheux Ah je n'ai aucun doute sur le fait qu'un phénomène astronomique bien-défini puisse être prédit à une précision de cet ordre (pour la rotation de la Terre, le facteur limitant la précision c'est la prédiction des irrégularités à long terme), …
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… I suspect the answer has something to do with the way SatNav signals reflect on the walls of various structures (rather than being simply absorbed), but I haven't been able to put 2 and 2 together and come up with an actual explanation. Does somebody know?
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… I can easily imagine why bad reception would lead to bad accuracy. I can even sort-of imagine why altitude would be harder to compute accurately than 2D position. But why does it always appear to be locating me ✽below✽ where I am, rather than above (in the air)? Why? …
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… By this I mean that my 2D position is roughly correct, but my altitude is somewhere around 50m to 200m below my correct altitude (which is just at ground level, so, easy to tell). This generally happens in narrow streets or limits of tunnels.␤␤This raises the question: WHY? …
I record a lot of SatNav tracks (SatNav = GPS + ГЛОНАСС + BěiDǒu + Galileo(?)), whether walking or riding, using OsmAnd on my phone, and I noticed the following pattern:␤␤‣ When reception is obstructed, my position is often reported as far ✽below✽ where I actually am.␤␤…
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@ngspiensfr @informatheux PS: Je suis quand même quasi-sûr d'une chose: on ne définit pas ce genre d'événements par un maximum ou minimum (de la déclinaison du soleil), c'est beaucoup trop imprécis: ce sera le moment où une certaine longitude ou ascension droite prend une certaine valeur cardinale.
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@ngspiensfr @informatheux … si bien qu'au final je n'ai jamais réussi à comprendre quelle était la «bonne» définition (ou si j'ai réussi, j'ai oublié), et je ne suis même pas sûr qu'il y en ait vraiment une.
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@ngspiensfr @informatheux … (du genre, prend-on le centre de la Terre ou le barycentre Terre-Lune? prend-on le centre du Soleil ou le barycentre du système solaire? pour l'équateur, prend-on l'axe du moment cinétique ou l'axe instantané de rotation? etc.) …
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@ngspiensfr @informatheux … qui est lui-même l'intersection avec l'équateur. Le problème est que chacun de ces plans (équateur, équinoxe, donc leur intersection) admet plein de petites variations dans sa définition selon les termes périodiques qu'on garde ou retire, et autres choix à faire …
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@ngspiensfr @informatheux À la minute près, je n'ai jamais eu l'explication, et je pense que c'est assez arbitraire: voir madore.org/~david/weblog/…␤␤Mais à qqs minutes près, le solstice est l'instant où le soleil atteint une longitude écliptique de 90° ou 270° mesurée par rapport à l'équinoxe, …
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@Jilcaesel (That was the joke.)
According to the Santa Claus Transparency Act, the Naughty List was supposed to be released on Friday, right?␤␤I guess they've checked it twice, now: so do we know who's on it?
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@Jilcaesel Well… 🤷 pic.x.com/UqJsoBmtR6
RT @ngspiensfr: If all you have is a hammer, everything looks like a nail, coder edition. pic.x.com/8xbVZ7rAzD
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@TheoremADayKDA “Flattery will get you nowhere but don't stop trying.” 😁
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@Jilcaesel Maybe we can try asking the resident AI. Hey, @grok, which X post can you find that has the smallest tweet id (=snowflake number) that is greater or equal to 2000000000000000000?
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@Jilcaesel I'd honestly be surprised if there weren't a spike of Twitter activity around 2025-12-14T00:28:52Z of people trying to hit the magic snowflake number. But of course this is hard to ascertain.
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(Et personne ne va lire, de toute façon. Mais il faut vraiment que je me décide à mettre ça sous forme de bouquin.)
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Bon, je vais vraiment devoir le couper en deux. Même comme ça c'est hyper long.
Le “billet” de blog sur lequel je travaille maintenant (et qui est le troisième d'une série sur les maths constructives) fait actuellement 27 pages (A4) en PDF, et il n'est toujours pas fini.␤␤💀
Who can find the tweet with the smallest tweet id that is ≥2000000000000000000 (2×10¹⁸)? (the quoted one is: 2000000033815777485). x.com/reallygalvin/s…
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[ Tweet id: #2001667510605652075 (Grok's answer) and #2000775214549160378 (original question). Also saved at: archive.is/uIf4k ]
Things are going great in the “public town square”. Nice atmosphere of trust and mutual confidence between the owner of the square, the “superhuman” AI and the “voice of the people”. Great ambiance. pic.x.com/pEURXvliXK
RT @Erivlt: Basically this: pic.x.com/uSty9dCVYj x.com/Cadyshaun1/sta…
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Basically, the strong order x⊲y means that there is a rational between the two. This turns out to be a very strong condition: it can't even be said in general that x ⊲ (x+1) (but of course 0⊲1, so the ‘⊲’ order can't even be said to be translation invariant). •9/9
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Also, x≤y is equivalent to ¬(x>y) and to ¬(x⊳y), as well as to ¬(x⋗y). For the Dedekind reals, ‘⊲’ and ‘<’ are the same thing (but ‘⋖’ remains different in general; and of course ‘≤’ is different even classically).␤␤This is a bit of a mess!␤␤•8/9
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One might call them the “strong”, “strict” and “weak” orders. And there is yet another one one might define:␤␤‣ (S,T) ⋖ (S′,T′) when (S,T) ≥ (S′,T′) does not hold.␤␤The implications are: x⊲y implies x<y which implies x⋖y which implies x≤y. None of them are reversible! •7/9
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… but the MacNeille cuts are far worse).␤␤There are three order relations one might put on them:␤␤‣ (S,T) ⊲ (S′,T′) when T∩S′ is inhabited,␤␤‣ (S,T) < (S′,T′) when there is d>0 rational such that S+d ⊆ S′ (where S+d is the translate),␤␤‣ (S,T) ≤ (S′,T′) when S⊆S′.␤␤•6/9
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Classically, (e) and (e⁻) are equivalent. Constructively, (a)–(e) define the “(Dedekind) reals”, whereas (a)–(e⁻) define the “MacNeille cuts” or “bounded extended reals”. They are not very well behaved (already Dedekind reals are a bit surprising w.r.t. classical math, … •5/9
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…␤␤(e⁻) ‣ any element less than one not in T is in S, and symmetrically: ∀s∈ℚ.∀t∈ℚ.((s<t) ⇒ (((¬(t∈T))⇒(s∈S)) ∧ ((¬(s∈S))⇒(t∈T)))))␤␤— which is constructively weaker than␤␤(e) ‣ if s<t then either s∈S or t∈T: ∀s∈ℚ.∀t∈ℚ.((s<t) ⇒ (s∈S ∨ t∈T))␤␤•4/9
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…␤␤(c) ‣ S is up-open and T is down-open: ∀r∈ℚ.(r∈S ⇒ ∃r′∈ℚ.(r′>r ∧ r′∈S)) et ∀r∈ℚ.(r∈T ⇒ ∃r′∈ℚ.(r′<r ∧ r′∈T))␤␤(d) ‣ any element of S is less than any of T: ∀s∈ℚ.∀t∈ℚ.((s∈S ∧ t∈T) ⇒ (s<t))␤␤— and crucially␤␤…␤␤•3/9
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A MacNeille cut is a pair (S,T) of subsets of ℚ s.t.:␤␤(a) ‣ S and T are inhabited: ∃r∈ℚ.(r∈S) and ∃r∈ℚ.(r∈T)␤␤(b) ‣ S is a down-set and T is an up-set: ∀r∈ℚ.∀r′∈ℚ.(r′<r ⇒ r∈S ⇒ r′∈S) and ∀r∈ℚ.∀r′∈ℚ.(r′>r ⇒ r∈T ⇒ r′∈T)␤␤…␤␤•2/9
I thought I was putting the finishing touches to a long blog post on constructive math, when I realized that I had very much misunderstood the order on the MacNeille cuts (aka “bounded extended reals”). In fact, there are at least THREE natural order relations on them! 🧵⤵️ •1/9
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x.com/gro_tsen/statu…
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My favorite, however, remains Sonder: The Realization That Everyone Has A Story. youtube.com/watch?v=AkoML0…
🚨 STOP EVERYTHING!␤␤Seven years after the last one, the “Dictionary of Obscure Sorrows” published a new YouTube video documenting an obscure sorrow: “Yráth: Hunger for Mystery in a Time of Easy Answers”.␤␤youtube.com/watch?v=sEi8qI…
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@Astatide42 @informatheux Sadly, no. (My workaround is more and more like “stop reading Twitter altogether, because the Good Place is better anyway.)
What makes this example really funny is that the geopolitical interpretation of “if you take the United States next to Cuba and replace Seychelles by Argentina you get Ukraine next to Russia” are actually pretty suggestive. x.com/gro_tsen/statu…
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So the initial combination of flags (“🇺🇸🇨🇺”) is:␤␤U+1F1FA REGIONAL INDICATOR SYMBOL LETTER U␤U+1F1F8 REGIONAL INDICATOR SYMBOL LETTER S␤U+1F1E8 REGIONAL INDICATOR SYMBOL LETTER C␤U+1F1FA REGIONAL INDICATOR SYMBOL LETTER U␤␤— and we replace “SC” by “AR” in this special alphabet.
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The reason is obvious once you know flag emojis are represented by the two-letter ISO 3166-1 alpha-2 name in a special alphabet: the flag “🇺🇸” of the US is represented by U+1F1FA REGIONAL INDICATOR SYMBOL LETTER U followed by U+1F1F8 REGIONAL INDICATOR SYMBOL LETTER S.
Some Unicode emoji fun I stumbled upon somewhere: if, inside the string “🇺🇸🇨🇺” (representing the flags of the US and Cuba) you replace “🇸🇨” (the flag of Seychelles) by “🇦🇷” (the flag of Argentina), you get “🇺🇦🇷🇺” (the flags of Ukraine and Russia). 😅␤␤Try it on a Unix system! ⬇️ pic.x.com/HJ3FLTfaiB
RT @joynessthebrave: There are a lot of dark things happening in the world. It is ok to draw back and not dwell on them, to focus on your o…
I'm with the wizard cat on that one. I couldn't decipher what it said until I read the bottom left image. x.com/RespectfulMeme…
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@laurentbercot @ngspiensfr OK, so that last part is something we agree with, and indeed something where my mental model of you was wrong. I apologize for that.
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@laurentbercot Just to be clear: for me, it's not “functional programming” so long as the closures aren't permitted to outlive the stack frame that created them (something that nobody is proposing to allow for C). The difference is the same as between exceptions and continuations.
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@ngspiensfr @laurentbercot … have no idea what the C standard means, so it did reassure me a little bit that the fact that my programs were so full of UBs wasn't entirely due to my stupidity (though you may disagree, of course).
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@ngspiensfr @laurentbercot … And I was not particularly trying to do stupid things, but it turns out that ~100% of all C code I wrote contains lots of UBs that I learned about later. What I learned by listening to people who do research in C semantics is that even they …
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@ngspiensfr @laurentbercot My belief that C is too complicated doesn't stem from what other people have told me but from my own inability to program in that language — and not for lack of trying. Granted, a good part of that is Unix's fault, not C's. …
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@laurentbercot … So my mental model of you predicts that you will respond by saying that programming is intrinsically difficult and that it's not your fault if idiots can't do it and that high-level languages are selling a pipe dream. Feel free to correct me if that mental model is way off.
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@laurentbercot … and you're so good at that, and also so specialized in only coding stuff for which you're good at, that you deride any attempt to make programming less demanding and/or less painful, by considering those you fail your bar idiots, and those attempts to help them, misguided. …
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@laurentbercot Condensed down to 3×280 chars, my mental model of you is that you write excellent low-level code because you're very good and incredibly patient at meeting the super high bar that the C language sets for paying attention to minutiæ that should be irrelevant in most cases, …
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@ngspiensfr @laurentbercot (But admittedly, I should have written “spec”, not “norm”, as the two are not entirely synonymous.)
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@laurentbercot So, is ⓒ a problem that can be fixed or one that cannot be fixed? Is it possible to isolate a decent subset of C that one can actually write code in, and which can be given a precise spec, one that it is understandable to humans and/or made formal?
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@ngspiensfr @laurentbercot The point of norms isn't necessarily to force people to do or not do stuff, it's to let them know what you recommend. “Don't Do Stupid Shit” isn't really helpful if you can't define or explain what C constructs or features are “Stupid Shit”. x.com/laurentbercot/…
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@laurentbercot … that is a satisfactory programming language to you, this is basically telling people that only you and your anointed can write good code and others can't even learn because the programming language with your blessing doesn't even exist except in your head.
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@laurentbercot … But your way of saying that ⓐ all languages except C are useless intellectual constructs that don't fix any real problem, ⓑ but even C is too complicated and those trying to make it evolve are wrong, and simultaneously ⓒ you can't even point to a well-defined subset of C …
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@laurentbercot … and more importantly, one in which what constitutes an UB is well-defined and understandable, instead of being a matter of reading a 700+ page standard plus errata and corrigenda, and can actually be tested algorithmically. …
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@laurentbercot In that case, what you should probably be doing is normalize your own language: a subset of C, presumably one in which you and others have already written lots of code, but with a clean, short and readable spec that removes cruft from C and adds guarantees in exchange, …
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@kebabroyal_ Let me add that every sufficiently old programming language contains the reluctant and badly designed addition of half of Algol-68. See also: cowlark.com/2009-11-15-go/…
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@JDHamkins @CmonMattTHINK In fact, if I'm not mistaken, even if we require all quantifications to be over a variable that actually occurs in the predicate, and allow an empty domain, we have the not-quite-obvious ?y.∀x.P(x,y,…) ⇒ ?y.∃x.P(x,y,…) where ‘?’ is either quantifier (same on both sides).
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@JDHamkins @CmonMattTHINK There are subtleties around the empty domain, as you pointed out earlier. For example, do we allow quantifying over a variable which doesn't appear at all? If so, for a 0-ary predicate P, we have ∃x.P ⇒ ∀x.P, but also ∀y.∀x.P ⇒ ∀y.∃x.P.
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@ArmEagle @bitsoffreedom I think breaching EU Regulations has become something of a goal in itself for Elon Musks's easily wounded ego. 🫤
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@laurentbercot I know how much you like to say that small is beautiful and so on, but when I have the editor of the standard (🔽) and also a friend we know (DM.*x) whose job is to work on a certified C compiler complain that this standard/language is a mess, I think I'm going to believe them. pic.x.com/Srbxay9mXC
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@laurentbercot While I acknowledge your expertise in system-level C, I think the editor of the ISO C standard working group (who, incidentally, is in no way a mathematician) is pretty damn qualified to discuss what C is for and what features it needs to adopt.
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Elon Musk is trying really really really hard to make me leave this site in disgust, but I'm not going to give him the satisfaction so easily. 🙃
Twitter has ONCE AGAIN started opening the disastrously bad “for you” tab by default instead of “following” that I use for my home feed.␤␤Is it just me or is this for everyone?␤␤Is it intentional or the result of yet another oopsie? (With Hanlon's razor it's hard to tell!)
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Let me summarize this some more: the s-m-n theorem causes security headaches on Linux. 🫠
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The whole sequence of events “C doesn't provide closures, but programming without them is simply insane, so people started using GNU-style nested functions, which create trampolines and require an executable stack, leading to security nightmares” is a parable until itself.
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See also this blog post by the same: thephd.dev/lambdas-nested…
The neverending quest to get closures/lambdas finally inside the C programming language: a detailed proposal, with context and discussion (and comparison with existing stuff), coauthored by JeanHeyd Meneide (project editor of the ISO C standard): thephd.dev/_vendor/future…
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PS: Since it's a “.gov” site, maybe it is prudent to donwload it locally before it gets replaced by an explanation that DEI is evil and charm quarks are a conspiracy by George Soros; fortunately, one can download it for offline use: pdg.lbl.gov/2025/html/comp…
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This site is, of course, better known for its listing of particle properties: pdg.lbl.gov/2025/listings/… — but there's lots of other interesting stuff there.
For many topics related to particle physics and high-energy physics (but not exclusively), there is a very interesting set of reviews in which one can learn lots of interesting physics (and even some math) at the Particle Data Group's Web site: pdg.lbl.gov/2025/reviews/c…
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And I have the same question for C (charge conjugation): if a particle (or particle system) is its own antiparticle, it has a C parity which is ±1 according as it is equal or opposite to its antiparticle.␤␤‣ How do we experimentally measure this?
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… I think I understand the math, but I have absolutely no idea about the following:␤␤‣ How do we experimentally measure P for a particle (e.g., hadron)?␤␤It's not like we can flip it in a mirror and see whether it changes sign!␤␤So, what are the real-world manifestations of P?
A quantum-mechanical system that has a plane of symmetry (e.g., a particle) has a “parity number” P which is ±1 according as the system is transformed into itself or its negative by the symmetry σ in question (i.e., the eigenvalue for which it is an eigenvector of σ). …
RT @pbeyssac: Confirmation sérieuse : le ministère de l'Intérieur a bien été piraté.␤␤Ce ministère souhaite :␤- le scan des messageries (#C… x.com/GrablyR/status…
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@liminaldoge @springbris ‣ Having a computer or a screen on a fridge MIGHT be acceptable or perhaps even useful.␤␤‣ Having/using an Internet connection on a fridge is useless, crazy and dangerous.␤␤‣ Using said connection to display ads is not only crazy, it is evil and dystopian.
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@CmonMattTHINK @JDHamkins This makes me wonder about the following combinatorics question: how many closed statements can we write by quantifying an n-ary predicate up to provable equivalence, and what is their order structure under provable implication?
UN CERISIER EN FLEUR EN CETTE SAISON‽‽‽␤␤(Créteil, vers la place du Palais.) pic.x.com/21zJpyhJxX
RT @DrToudou: DERMATOSE NODULAIRE CONTAGIEUSE BOVINE␤␤Bon. Vous me faites chier. Faut que je retourne au charbon. C‘est le bordel sur les r…
So many Canadian immigrants in France! 😶 pic.x.com/zyCuHe149c
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Quelques vues prises en chemin pic.x.com/m5nmOfoJZU
Inauguration du #Cable1 d'Île-de-France à Villeneuve-Saint-Georges pic.x.com/mQTllOjMQa
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The funny thing is, I learned this because my mother showed me a page from the local newsletter of the city of Orsay about the IHÉS, which mentioned Kontsevich and said in passing that he had proved that most cubic hypersurfaces in dimension 4 aren't rational — so I went “WHAT?”.
Somehow I had missed the news that very general cubic hypersurfaces of dimensions 3 and 4 are now known not to be rational. (See arxiv.org/abs/2510.13679 for statements, references and context.)
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There are like a gazillion captions you could write on this photo just starting with: “So I said to him/her…” Go ahead, try it. pic.x.com/I6OpcOmQlI
They say a picture is worth a thousand words, but this photo of Steve Bannon and Noam Chomsky apparently being great pals at an event organized by Jeffrey Epstein is worth a thousand snarky comments on the topology of the political spectrum and the mores of intellectual élites. x.com/mtracey/status…
RT @GGrundin: @gro_tsen The FIFA physics prize is not a real FIFA prize. The full name is ‘the Prize in Physical Sciences in Memory of FIFA…
I didn't follow the news too closely: has the winner of the FIFA physics prize been announced yet?
People keep talking about the autism spectrum, but what are its homotopy groups? 🤔
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(I wrote this in Times font because it needs to be very professional. Also, contrary to the government of a certain 30T$-GDP country, I know how to set up font ligatures correctly.) x.com/gro_tsen/statu… pic.x.com/jk2gjUVoJ7
🚨🎅 In this season it is important to know your 🇪🇺 GDPR rights!␤␤The following template letter might be of use, especially if you suspect that you have been placed on the so-called “naughty” list: ⬇️ pic.x.com/AfGJcP7yUV
RT @AutismCapital: >Be Australia␤>Tell users you need them to ID verify to avoid stalking and cyber grooming␤>All the data gets leaked␤>The…
pic.x.com/Aw9LQ9wroq x.com/AutismCapital/…
RT @wikihow_museum: cher père noël,␤urgent. vous allez perdre vos droits CPF. consultez votre budget et réclamez votre formation 100% prise…
À partir de maintenant, à Paris, le Soleil se couche de plus en plus tard. explainxkcd.com/wiki/index.php…
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Not only that, but the word “Rwanda” and the “ans” in “my fellow Americans” is rasterized in a DIFFERENT way (blurry rather than pixellated). Indeed, if we extract the PDF images, we find a layer with these patches. ↘️ WTF happened here? pic.x.com/OU57dtoEW2
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But perhaps the most bizarre part of this document is the foreword(?) by the president. Ignoring the half-page-sized signature, which I guess is part of the current president's… well, signature, the strange thing here is that it's rasterized. It's a bitmap image in the PDF! 😲 pic.x.com/tCG9KK8Qke
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And you should probably justify the right margin. pic.x.com/rfYPb1WM06
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Also, if you want your document to look professional, it's not enough to use Times New Roman, you should also learn how use the ligatures (I'm talking about “fi” here, TNR doesn't have an “st” ligature). pic.x.com/rn6IRHzLDw
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But just look at the dots on this table of contents! Why does every line seem to have a different spacing of dots? And why do the letters in section (IV)(3) have a much wider spacing after them than the numbers of the higher-level divisions? This is very sloppy. pic.x.com/SfJpcRuJle
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The document is here: whitehouse.gov/wp-content/upl… Admittedly, its first page is fine. Which only serves to better contrast what follows. pic.x.com/WVuZgcuJTP
An ironic twist to the sudden preoccupation of the US State Department for typographic professionalism is that the Administration just published its official (2025) National Security Strategy document, and, purely from the typographical point of view, it is incredibly amateurish. x.com/gro_tsen/statu…
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@Conscrit_Neuneu This particular post was linked on Reddit.
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(Both statements are classically true, but they are so trivially true that one tends to wonder “wait, did I misunderstand?”. Constructively, they are unprovable, and have some interesting consequences.)
Constructive math tends to consider statements that give classical mathematicians a headache, like:␤␤‣ “For every subset S⊆{•} of a singleton there is a real z∈ℝ s.t. S = {• : z>0}.”␤␤‣ “For every z∈ℝ there is a binary sequence b∈{0,1}^ℕ s.t.: z>0 iff ∃i.(b_i = 1).”
Unlike the rest of the country, the US military does some sane things like use a 24h time and count distances in metric. So of course the military-obsessed Americans respect these standards and their use…␤␤…just kidding of course: it's “stolen valor”. 🤣 linkedin.com/posts/kevinhal… pic.x.com/LScCSFgIs2
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10 heures plus tard (😫), je pense avoir tout remis en place comme c'était.
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@fclimence Des recommandations d'hébergeurs sur machines dédiées dans le même ordre de grandeur de prix?
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@pbeyssac Oui, c'est exactement ce qui se passe, je pense. Je soupçonne que c'est juste l'alim qui pose problème, mais je n'ai évidemment aucun détail: ils disent juste «voilà, on vous en a attribué une nouvelle» (et je perds 3j à tout réinstaller).
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J'ai basculé sur le serveur de secours que je garde en standby, mais il y a probablement plein de choses cassées sur mon site, du coup.
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Précédemment: x.com/gro_tsen/statu…
La machine Scaleway Dédibox hébergeant mon site Web est ENCORE MORTE. 😖␤␤(Première machine mise en service le 2014-10-21 et morte le 2020-10-05, sa remplaçante morte le 2022-04-12, la suivante le 2024-11-11, la suivante le 2025-01-14, c'est donc la 5e qui meurt en 5 ans. 😮‍💨)
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There: fixed it for you. Don't you think Twitter looks so much more professional and so much less woke in Times New Roman font? 😐 pic.x.com/fBFCG0284N
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Also, perhaps someone needs to notify Elon that his site is woke, 'cause I don't see the serifs. pic.x.com/uS98Sr1Xjn
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youtube.com/watch?v=cISYzA…
Apparently sans-serif fonts are woke diversity, now, and real men use Times New Roman for “professionalism”. 😂 x.com/Phil_Lewis_/st…
@GenevieveMadore Tu devrais aimer: x.com/pawcord/status…
I am lost in a maze of twisty little logical formulas, all alike. pic.x.com/39sGJ7xq9U
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Apparently I'm NOT the only one affected by this, because my bug has been closed as duplicate: bugzilla.mozilla.org/show_bug.cgi?i… x.com/gro_tsen/statu…
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@Banlieuedeprof Ce livre de maths niveau collège n'est pas mal non plus: pic.x.com/wQZbW4Czrn
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@HW_Tra @Banlieuedeprof 🧵🔽 x.com/gro_tsen/statu…
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Lien direct: ec.europa.eu/info/law/bette…
@GenevieveMadore Si tu n'y as pas déjà répondu, cette consultation publique de la Commission européenne sur le bien-être animal devrait t'intéresser: fondation-droit-animal.org/guide-de-parti… (contrairement à >99% des pétitions que tu relaies, c'est sérieux, et ça peut avoir un impact).
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@kebabroyal_ Well, if you're going to state it that way, then classical mechanics also doesn't exist, it's just an approximation of QM. 🤷 We still generally think of it the other way around. But I don't care. My point is that there are three levels (so two comparisons to make).
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@kebabroyal_ … whereas ①→② brings a quantization of amplitude (because waves can only come in discrete amounts).
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@kebabroyal_ For light, it is remarkable that ⓪→① brings a quantization of frequency (if you take a standing EM wave between two parallel mirrors, its frequency is quantized, while geometrical optics puts no constraints on frequency, which is why I say Maxwell's equations are “quatum”), …
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@kebabroyal_ … For light: ⓪ classical light particles or geometrical optics → ① Maxwell's equations → ② quantized E-M field.␤␤For electrons: ⓪ classical point charged particles → ① Schrödinger or Dirac → ② quantized version.␤␤The question is why ①→② looks so much like ⓪→①.
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@kebabroyal_ By a “classical photon” I mean the historical conception of light as point particles. But take geometrical optics if you prefer: this is unquestionably a well-defined theory, and Maxwell's equations are a first quantization of it. There are really two steps. …
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@kebabroyal_ … And regardless of whether you call them “quantization”, there is a first step that takes a classical point particle to a field (which I say describes a quantum particle), and a second step that takes a field to a quantum field. And each step linearizes.
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@kebabroyal_ I disagree. Maxwell's equations describe a classical FIELD, but a classical field is already a quantization of classical PARTICLES (classical light point particles). Exactly the same holds for Schrödinger, Klein-Gordon, Dirac, Yang-Mills, you name it. …
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I still think it would be a great feature if we could also launch multiple Firefox Android activities (each with multiple tabs) like one can launch multiple windows on desktop, so the Android task list/button/gestures would let us switch btw them.
I just discovered accidentally that in Firefox Mobile for Android (at least on version 146) one can switch between tabs by swiping left or right on the top bar (the one with the URL in it).␤␤I lost so much time going to the tab list page every time I wanted to switch tabs! 😮‍💨
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@kebabroyal_ … Which appears to be true, and indeed strongly constrains things, but it is still a mystery why we TWICE need to make something nonlinear linear by quantizing it.)
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@kebabroyal_ (What I mean is: the unstated physical assumption in what you — or Weinberg — say is that QM needs to remain exactly linear, so we are looking at linear reps of the Poincaré group, not its action on the solution space of a complicated nonlinear PDE. …
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@kebabroyal_ … to interact, you lose linearity; and quantizing a second time restores linearity by making the space of states a (monster) Hilbert space or something. So nature seems to really enjoy making nonlinear equations linear and maybe that's what quantizing is all about.
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@kebabroyal_ Indeed, and I think the following is part of the puzzle (or its solution?): you start with classical mechanics for N noninteracting point particles in a fixed potential well — this is nonlinear. Quantizing it makes it a linear wave equation. Now if you want the particles …
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@kebabroyal_ … I mean photons are not vibrations of some other quantum particle like phonons are vibrations of quantum atoms/electrons, so why do they behave as though they were? I don't think any amount of math can answer this.
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@kebabroyal_ I think I see what you mean. But you can't deny that there is a real ❋physical❋ mystery to the fact that real (supposedly) elementary particles behave in the same way as phonon quasiparticles which are indeed vibration waves on coupled quantum oscillators. …
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@IanSolliec Just follow me on Bluesky instead. 😝
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Ooops, the start of the first tweet in the thread was mangled as I copy-pasted from the Good Place.␤␤It should read: Many people seem to think that quantum mechanics, i.e., “first quantization” is a mys— x.com/gro_tsen/statu…
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(Disclosure: I admit I'm purposefully playing stupid in a few places here: I understand this better — or less badly — than this thread suggests. But I think it helps to explain things dumbly, and I honestly don't understand why nobody seems to point out how WEIRD it is.) •16/16
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… also: why are so many videos, essays and popular science stuff dedicated to trying to explain the philosophy and intuitive ideas of the FIRST quantization, and absolutely NONE about this completely mind-boggling fact that FOR SOME REASON WE NEED TO DO IT A SECOND TIME? •15/16
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… and also why are we doing the whole process just TWICE? (why is there no THIRD quantization? how do we know there isn't? would it make sense?) and how did people realize that they had to do this? and why was their mind not completely blown to pieces when they did? … •14/16
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… (well, the same math except for the ever-so-tiny problem that we now have one fictitious particle per point in space, so, continuum-many of them, so there are infinities all over the place and it's a mess… but even in discrete space I find this SO mysterious); … •13/16
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This raises so many questions, like: what are these fictitious particles (field values) supposed to represent? what are they vibrating into? if this is just a mathematical ploy, by what coincidence is it the EXACT SAME “QUANTIZATION” MATH that was used the first time? … •12/16
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How in the world does it make any sense that, just after we made particles into waves, we imagine the waves as oscillations of fictitious particles at every point in space in fictitious dimensions AND THEN QUANTIZE THAT AGAIN, FOR FUN? and it works??? •11/16
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… because the vibrations of a quantum mechanical oscillator are discrete (a wave in a potential well can have only discrete oscillation modes), so I get some sense of why this makes discrete particles reappear, but — dude — what the F😵‍💫CK did we just do there??? and why? •10/16
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… and then we have to imagine somehow taking the continuum limit of this unimaginable system of one-oscillator-per-point-in-space, and this is what a “quantum field” is. So maybe, just maybe, I can imagine that this makes the discrete particles reappear in a sense, … •9/16
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… except that NOW WE APPLY THE SAME QUANTIZATION PROCEDURE (used in 1st quantization) that takes an ordinary harmonic oscillator (pointlike particle) into a quantum wave equation, and we apply it to each one of these fictitious oscillators at EVERY POINT IN SPACE, … •8/16
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… (like imagine a bunch of masses connected together by strings, except that there's a mass at every point in space and they're vibrating in a completely unrelated dimension): this is already a weird idea, but, yeah, it's the same equation so we might see it like that, … •7/16
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… so, we take this wave equation that comes out of the 1st quantization, now we observe that, if we discretize space, we can imagine the wave equation as a bunch of oscillators vibrating in a FICTITIOUS “field” dimension, and coupled so waves can propagate through them … •6/16
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… “so you know how we just turned pointlike particle into waves in a field? psych! we'll now turn them back into particles — kinda sorta — by quantizing the field itself!” And nobody discusses how insanely weird this is (and even the math is very poorly understood): … •5/16
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… but these wave equations, whether Maxwell's equations for photons or Schrödinger's equation for (nonrelativistic) electrons aren't really weird. We've all seen waves around us (e.g., water ripples). What I find incomprehensible is the SECOND quantization, which says: … •4/16
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… that Newton & others had imagined, nobody was really surprised, nobody found this horribly counterintuitive. Maxwell's equations are the 1st quantization of pointlike light particles. No big deal. Yes, this causes weird effects like interference and stuff like that, … •3/16
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You start with classical mechanics of pointlike particles. The FIRST quantization turns this into a wave equation (i.e., “particles are waves after all”). Now I agree that for electrons this is surprising, but when Maxwell turned into waves the particles of light … •2/16
tery and that “second quantization” (i.e., quantum field theory) is not (it's a common adage: “1st quantization is a mystery and 2d quantization is a functor”). I disagree! Let's recap: 🧵⤵️ •1/16
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… (WHICH WAS THE ENTIRE POINT OF THE PUBLICATION PROCESS IN THE FIRST PLACE) resort to various social media, including, apparently, comments on YouTube videos. 😭
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To caricature slightly (but only slightly): because the formal scientific publication process is used to evaluate researchers, it needs to be tightly guarded, and because of this, researchers who actually need to communicate between themselves …
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(The comment in question is here: youtube.com/watch?v=zb17Nh… )
Seen on MathOverflow (and paraphrasing): “I've outlined the flaw in <such-or-such result from the literature> in a comment to the following YouTube video”. 🫤
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@antoineducros Euh… vraiment? Il me semblait que c'était en réfléchissant au théorème de Belyi [Belij] qu'il avait imaginé cette façon de représenter les choses. Figuration d'ailleurs assez naturelle puisque Klein l'avait déjà inventée ~100 ans avant (mais apparemment Grothendieck l'ignorait).
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@laurentbercot You mean like that one time in 2014 when my enter key stopped working (only) in the URL bar of Firefox on my 32-bit machine and it turned out to be because I had a libc5 lying around which a JS hook stupidly tried to load and struct dirent didn't match? 😅 madore.org/~david/weblog/…
Note that Mendeleev seems to have discovered the periodic table because he was trying to decide how to best organize the elements for his book.␤␤I think this is a beautiful example of how teaching can lead to research-level discoveries. x.com/gro_tsen/statu…
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On the history of the periodic table, and the precursors to Mendeleev: youtube.com/watch?v=0p6cpV…␤␤(I only regret that this video doesn't delve into the difficulty dealing with transition metals, and, worse, the lanthanides. When were they correctly organized?)
This leaves me wondering whether I might actually be the only person on Earth using Linux + X11 + fvwm2 + Firefox ≥145 + a 2012-ish graphics card with the “r600” Mesa driver.␤␤Like: this is a but targeting ME SPECIFICALLY. 😵 x.com/gro_tsen/statu…
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In some cases (e.g., if I disable hadware acceleration), main UI is unaffected, but there is still a displacement of all tooltips that Firefox displays (e.g., on some links) after entering and leaving fullscreen mode.␤␤Still investigating, but attempts to reproduce are welcome!
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Update: preliminary tests suggest that this is a VERY specific interaction between fvwm2 (the bug doesn't happen with icewm, fluxbox, openbox), Firefox ≥145 AND possibly the hardware acceleration of my very specific card (Radeon HD 6450 Caicos, using the “r600” Mesa driver). 😫
RT @wikihow_museum: - et là je coche quoi du coup, « je ne suis pas un robot » ? pic.x.com/zyA95MhogQ
RT @yarotrof: @EmmaMAshford Imagine if the EU had issued a paper saying that its strategic priority is the breakup of the United States int…
RT @yarotrof: And the talk in Washington about the “unpopular and unelected” Brussels bureaucracy is completely uninformed by public opinio… x.com/yarotrof/statu…
I am encountering an extremely annoying bug with Firefox (145 through 147) under Linux + X11 + fvwm: bugzilla.mozilla.org/show_bug.cgi?i…␤␤Basically, if I enter and leave fullscreen mode, everything in the window is shifted by ~30px, including mouse clicks.␤␤Can sbd reproduce?
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I ask because all sources cited by Wikipedia en.wikipedia.org/wiki/History_o… appear to be written by journalists, amateur/hobbyists, or computer science academics, not by actual historians.␤␤Is this bias on the part of Wikipedia, or on the part of historians? 🤔
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This makes me wonder: are there academic historians (=researchers in academic institutions whose primary field is History) who specialize in the history of software, or operating systems specifically, in the 1950–1990 interval (roughly)? Any books or publications I might read?
It seems someone found a magnetic tape at the University of Utah that may contain the only surviving copy of version 4 of Unix Operating System from Bell Labs (circa 1973): youtube.com/watch?v=IR-f07… 🤩
RT @SwiC_RC: Ma conception de la culture c'est pas « cette série est super ; tu veux la voir ? abonne-toi à Netzon+ » mais plutôt « tu veux…
OK, I… think I will have to see this movie. imdb.com/title/tt323213…
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… it's that simple. If the “closer is better” principle were true, I'd want to be ruled by Parisians only. 🤷 (But really, I'd like the EU, France and Île-de-France region to have roughly equal power over me, in the spirit of governmental “checks and balances” & subsidiarity.)
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Also, on a more serious note, I never understood the argument that I should feel better represented by the French, or happier to be ruled by them, just because I myself am French. Several other EU countries just seem better run to me, so I'm happy to let them have a say, …
Let me get this straight: this American, Canadian and South African citizen is lecturing me, a French (and Canadian) citizen, that German, Italian, Spanish and Polish citizens shouldn't be lecturing me about how France is run because they are “foreign”. Did I get this right? 🙄 x.com/elonmusk/statu…
RT @GovPressOffice: WOW! AN HONOR! — GCN pic.x.com/93QmN531X5
RT @Jilcaesel: pic.x.com/hNRcVaEjqE
RT @NithurM: This new Cloudflare landing page is wild. pic.x.com/Bxq8gpDGd4
RT @CSMFHT: pic.x.com/VR3stmStyS
RT @dieworkwear: The Nobel Prize committee should announce the World Cup winner tomorrow.
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En tout cas, le discours encourageant à renoncer à la voiture individuelle, quand il est quasi impossible de louer une voiture ponctuellement, il a du mal à passer.
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(L'explication, c'est que les voitures se font vandaliser. Donc ils délaissent les quartiers plus populaires. Ou peut-être qu'il y a une taxe pour franchir l'enceinte des Fermiers généraux, allez savoir.)
Décidément, l'autopartage, économiquement, au moins à Paris, ça ne marche pas. Après je ne sais combien d'abandons, faillites, rachats, reculades ou fusions (Autolib 😢, Ubeeqo, Car2go, Share Now…), un des seuls acteurs restants (Free2Move) recule encore sa zone de couverture. pic.x.com/IGt0ONuuCB
RT @gro_tsen: @monsieurpuyo If this universe is a simulation, we must be living in the “mandatory unskippable ad break” part.
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@monsieurpuyo If this universe is a simulation, we must be living in the “mandatory unskippable ad break” part.
There is NO WAY anyone could have guessed this! 😶 pic.x.com/s6TbhfWiap x.com/atrupar/status…
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(I think “chemists look down at Lie group theorists because they look at the diagram for isobutane and think it represents sulfur octoxide” might be heading towards the most niche joke ever.)
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On the other hand, it is true that chemists are better at creating complicated molecules while mathematicians are somehow obsessed with acetylene, but-2-ene, 3-metylpentane, 3-metylhexane and 3-metylheptane. 😔 pic.x.com/oi4q4MDeVo
Mathematicians are so much better than chemists because chemists only study SO₂ and SO₃ whereas mathematicians study SO_n for any n.
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This is from: arxiv.org/abs/math/04035…
😬 pic.x.com/GCZ79bBsb2
Just a friendly reminder that, despite the name, Fabergé eggs are NOT TO BE EATEN: bbc.com/news/articles/…
Gratuitous artistico-mathematical image (interlaced lines with 7-fold symmetry): pic.x.com/FLWidcdJFU
RT @ngspiensfr: Do you use #GMail?␤It seems at some time recently, they stopped showing you delivery status notifications: that means GMail…
RT @le_gorafi: La poule ayant pondu l’œuf lancé sur Jordan Bardella sera expulsée de France legorafi.fr/2025/12/03/la-…
More fascinating books that I'll probably never have the time to read. pic.x.com/caDefgf8jZ
RT @CompSciFact: The C code below compiles and prints "hello, world". pic.x.com/ezmB2A335a
RT @pbeyssac: Comme à peu près tous les mois. (source : bonjourlafuite.eu.org)␤␤Mais on nous explique par ailleurs que collecter l'âge de… x.com/Numerama/statu…
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(À partager surtout si vous connaissez des gens qui travaillent dans le secteur bancaire, ou avec des contacts avec une association de consommateurs susceptible de s'intéresser au sujet.)
Des explications sur le fonctionnement du crédit renouvelable, le calcul du TAEG, le caractère usurier de certaines offres, et les limites de la réglementation. 🔽 À partager largement!␤␤(Full disclosure: l'auteur est mon copain.) x.com/Conscrit_Neune…
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… there is no credible real-life scenario in which you would get an information such as “there is ≥1 ace in this hand of cards” without getting the extra information of what specific card is an ace and/or which ace it is.
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One of the reasons which makes this question so confusing and counterintuitive is that the notion of “conditioning” (conditional probabilities), while mathematically simple, doesn't always correspond to a plausible real-life scenario (namely, acquiring information): …
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… But if you specify “the hand contains the ace of spades”, now there are only 2 possible hands left, and the chances of having a second ace are now 1/2.␤␤This is reminiscent of the super famous “Monty Hall (goat) problem”: en.wikipedia.org/wiki/Monty_Hal…
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If you're still not enlightened, consider a deck with only 3 cards: the ace of spades, the ace of foobars and the jack of potatoes. Draw two cards randomly (only 3 possibilities!). There is necessarily at least one ace: your chances of having a second one are 1/3. …
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To put it differently, by saying “the hand contains the ace of spades”, we restrict by a factor 4 the number of hands containing EXACTLY ONE ace, but by a smaller factor those containing 2, 3 or 4 aces (the latter isn't restricted at all), so they become relatively MORE probable.
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… but remember this: with the info “there is an (≥1) ace in hand”, “the ace” does not refer to a well-defined card: so “the ace of spades is in hand” is NOT independent from “there are ≥2 aces”: the more aces there are, the more likely a randomly guessed suit (spades) works!
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But why? Well, the fact that p₁=p₃=p₄ makes sense: given that the leftmost card is an ace, its suit is irrelevant (p₃=p₄), and given that the ace of spade is in hand, its position is irrelevant (p₁=p₃). The fact that p₂<p₁ is more surprising, …
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So: given any one of the data ①“the ace of spades is in hand”, ③“the leftmost card is the ace of spades” or ④“the leftmost card is an ace”, the probability of having ≥2 aces is p₁=p₃=p₄≈22%; BUT given ②“there is an ace in hand”, it's only p₂≈12%.
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… The second is slightly more tricky: there are binomial(48,5) unordered hands with no ace in them, so binomial(52,5) − binomial(48,5) unordered hands with at least one ace, and binomial(48,4) × 4 unordered hands with exactly one ace.)
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(Justification: let's say we count unordered hands for ease of notation. The first is an easy count: there are binomial(48,4) ways to choose 4 unordered non-ace cards, and binomial(51,4) ways to choose 4 cards other than the labeled ace. …
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The answer is that: p₁=p₃=p₄ > p₂. In fact:␤␤p₁ = p₃ = p₄= 1 − binomial(48,4) / binomial(51,4) = 1 − (48×47×46×45)/(51×50×49×48) = 922/4165 ≈ 22.1%␤␤p₂ = 1 − (binomial(48,4) × 4) / (binomial(52,5) − binomial(48,5)) = 2257/18472 ≈ 12.2%
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How do you think p₁, p₂, p₃ and p₄ relate?␤␤Which are equal to which, and in which order are they?␤␤(Answer in the next post.)
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(Precisely: if X is the set of 5-uples of distinct cards in a standard 52-card deck, Y₁ those containing the ace of ♠, Y₂ those containing ≥1 ace, Y₃ those starting with the ace of ♠, Y₄ those starting with an ace, and Z those with ≥2 aces, then p_i := |Z∩Y_i| / |Y_i|.)
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We can add more!␤␤③ Randomly draw 5 cards from a deck of 52. Knowing the LEFTMOST is the ace of spades, let p₃ be the prob that there are ≥2 aces.␤␤④ Randomly draw 5 cards from a deck of 52. Knowing the LEFTMOST is an ace, let p₄ be the prob that there are ≥2 aces.
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This thread is, in fact, based on an earlier Twitter thread, which had a poll attached, so I know that most people (at least on my then Twitter followers) think p₁=p₂. But this is wrong!␤␤x.com/gro_tsen/statu…
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(To be clear, p₁ is the conditional probability of having ≥2 aces in hand under the condition that the ace of spades is in hand, and p₂ is the same under the condition that ≥1 ace is in hand.)␤␤Would you say p₁<p₂, p₁=p₂ or p₁>p₂?␤␤Think before you read on!
① Randomly draw 5 cards from a deck of 52. Knowing the ACE OF SPADES was drawn, let p₁ be the probab that there are ≥2 aces in hand.␤␤② Randomly draw 5 cards from a deck of 52. Knowing that SOME ACE was drawn, let p₂ be the probab that there are ≥2 aces in hand.␤␤🧵⤵️
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@JacqBens Ah, actually it doesn't seem to depend on the exact words, only on how many there are. This is a bit less bizarre, I guess.
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@JacqBens The utterly bizarre thing is that it happens if I search for “from:@gro_tsen third law politics”, but if I omit any one of the last three words, I get reasonable search results. How‽ Why‽ pic.x.com/3fnVxYOg9v
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@YogiYogui Maybe it depends on the interface language or user account or some other parameter, because it keeps giving me random stuff (in the “latest” tab — the “top” tab is good): pic.x.com/XLq1gCLUDe
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Link to search: x.com/search?q=from%…
I remember a time when searching Twitter for “from:@gro_tsen some words” would actually return tweets by @gro_tsen containing some words, not just… random unrelated stuff. pic.x.com/bgrmImhd1L
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E.g., while the middle-ground fallacy (assuming that the truth necessarily lies “in the middle”) is quite real and serious, it is just as fallacious to refute any middle-ground position by saying “middle-ground fallacy”.
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(And yes, before someone points this out and thinks they're very clever, this can apply recursively, but the fallacies become rarer and rarer as you pile on the meta levels, so we can safely ignore the higher ones.) x.com/gro_tsen/statu…
It is worth keeping in mind that for each logical fallacy there is a corresponding (if generally rarer) meta-fallacy which consists of wrongly accusing someone of committing the fallacy in question when hearing a superficially similar (and perhaps correct) reasoning.
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The history of paracetamol (=acetaminophen), and why we still don't know how it works. youtube.com/watch?v=mqJOgA…
🧵🔽␤␤(Heureusement que la coche bleue «compte vérifié» nous protège contre les bots voulant se faire passer pour des humains. 😂) x.com/LYMFHSR/status…
Je n'en reviens toujours pas que l'expression «lutte des classes» ait été pondue par François Guizot, of all people.
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(Je parle au passé parce que je suppose que de nos jours, vouvoyer ses enfants doit être devenu extrêmement rare, même dans la très bonne société. Mais peut-être que je me trompe!)
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Plus généralement, selon l'époque, dans les classes sociales supérieures (aristocratie et haute bourgeoisie), dans quelle(s) condition(s) vouvoyait-on ses enfants?␤␤(Je parle de gens qui vont clairement vouvoyer leurs parents, dont c'est la réciproque qui m'intéresse.)
Dans “Le Rouge et le Noir”, je remarque que le Marquis de la Mole tutoie son fils Norbert mais vouvoie sa fille (non mariée) Mathilde.␤␤Était-ce l'usage à l'époque?
RT @SaarelaHC: Highland Cattle photo of the day pic.x.com/hovsTyyr31
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@dioscuri pic.x.com/Ffgj2v1xUO
RT @dioscuri: Roughly 99.99% of games of Go ever played are AI self-play training games. So if you ever find yourself playing Go that means…
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We can avoid referring to “this statement” by Quine's trick:␤␤‣ CLAIM: If the following quoted words followed by themselves between quotes are true, then pigs have wings: “If the following quoted words followed by themselves between quotes are true, then pigs have wings.”
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If you're confused: this is known as “Curry's paradox” en.wikipedia.org/wiki/Curry%27s… — if a statement (A) is equivalent to the fact that it implies another (B), then B is, in fact true. Or, provocatively, if we can make the sentence “if this sentence is true then B”, then, in fact, B.
THEOREM: pigs have wings.␤␤Proof:␤␤‣ CLAIM: if I'm right about this, then pigs have wings.␤␤‣ Clearly, if I'm right about this claim, then pigs have wings.␤␤‣ But that was the claim. So I'm right about this.␤␤‣ So pigs have wings. ∎
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‣ See also: “Hanlon's razor” en.wikipedia.org/wiki/Hanlon%27…
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… The sad reality of the world is that there are no secret evil overlords pulling strings from the shadows according to a sinister plan: we are ruled by the exact same bumbling idiots and incompetent cowards who appear to be in charge, and who have no idea what they're doing.
One thing all conspiracy theories seem to have in common is the belief that the people in charge are actually very smart and competent (if for nefarious purposes). This thought is, at some level, comforting: for my part, I'm too pessimistic to believe such things. …
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@tak3sh8 PS: on the story of the “Scottish Book”, and how a live goose came to be attached as a reward for this problem: 🔽 x.com/gro_tsen/statu…
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A history of Stefan Banach &al's celebrated “Scottish Book”, and of interwar Polish mathematics in general. youtube.com/watch?v=4K7WVt… [For some reason the YouTube vignette doesn't display, so I'm putting a screenshot below.]␤␤PS: If you want to read it → link.springer.com/book/10.1007/9… pic.x.com/OirT2IE0Jm
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@henriparisien Peut-être, mais le RGPD, qui est un règlement européen, prime sur Hadopi, qui est une loi française. (Et dans la pratique, plein d'endroits ignorent cette obligation.)
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The above must be an attempt to perform the most French theft of all times.␤␤Meanwhile, the most Canadian theft ever remains this: en.wikipedia.org/wiki/Great_Can…
Only in 🇫🇷: 90k€ worth of snails stolen. bbc.com/news/articles/…
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En gros, en fait, vous êtes en train de souligner le fait qu'on ne capte pas bien la 5G dans certains coins de vos centres commerciaux, et je ne sais pas si c'est tellement à votre intérêt.
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D'une part, mettre des conditions à la con comme ça pour accéder à un wifi, en 2025, c'est invraisemblablement pingre et mesquin, d'autre part exiger des gens de donner une adresse mail pour les abonner à une liste de spam pour accéder à un service, c'est pas super RGPD je crois.
Les centre commerciaux Westfield (au moins Vélizy 2 et Parly 2) ont un wifi qui laisse le choix entre vous 20min gratuites à condition de s'abonner à leur liste à spam, ou bien illimité à condition de rejoindre leur club avantage chépakoi.␤␤On se croirait en 2005, là. 💩
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A history of the development of the implosion-type plutonium core nuclear weapon by project Manhattan (why the plutonium bomb needed to be made this way, why it was so complicated, and what role John von Neumann played in the story): youtube.com/watch?v=W06g7g… Fascinating!
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@antoineducros Je pense que «vulgus» a été compris à tort comme un adjectif, et du coup ce serait «vulgum» parce que «pecus» est neutre.
#AujourdhuiJaiAppris que «vulgum pecus» n'est pas du bon latin («vulgus» est un nom, pas un adjectif, l'adjectif est «vulgaris»), et ne s'utilise en gros qu'en français. pic.x.com/bxMmVuIcS0
RT @PDLComics: always be there pic.x.com/lTEklno6R9
RT @PDLComics: microwave pic.x.com/QJD5X6cvuH
A cheat sheet with a few infinite sums that can come in handy (here, G is Catalan's constant, and μ is the Möbius function): pic.x.com/LCidtuhk9q
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@rperezmarco This is amazing! Please tell me when you have a publicly available version of your historical paper, I will be very interested to read it.
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(I have a hard time reading the handwriting, so we'll have to wait until published version, but Mittag-Leffler starts by saying he doesn't recall the conversation, and even if it did take place, Borel misunderstood what he meant.)
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Second update: in a startling development, we now have Mittag-Leffler's side of the story as well, thanks to a handwritten draft that he left in his personal copy of Borel's book just where B. recounts the episode! x.com/rperezmarco/st…
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@rperezmarco 😲 You had my curiosity, now you have my attention! So, what was Mittag-Leffler's own version of the episode?
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Update: the anecdote above is in fact misreported. While it is true that Mittag-Leffler refused to listen to Borel because “the master said so”, it was on a different topic (monogenic functions), and ”the master said so” is not a direct quote. x.com/rperezmarco/st… pic.x.com/9981O9Ypl2
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Incidentally: in his Wikipedia photo, Mittag-Leffler has an absolutely badass look befitting the arch-villain in a steampunk universe.␤␤I don't care what other candidates are proposed, he HAS to be an inspiration behind Doyle's character of Professor Moriarty. pic.x.com/SWV2NN8MyD
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Also a bit hard to reconcile with the fact that (per the same Wikipedia article), there is a Mittag-Leffler summation of divergent series, which generalizes Borel's. en.wikipedia.org/wiki/Borel_sum…
Great anecdote, but doesn't reflect very well on Mittag-Leffler's character. pic.x.com/WCm3eGvhe6
RT @KyleKulinski: pic.x.com/TF1X9R9mTP
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Notez que l'employeur a très bien pu lui-même faire appel à une IA pour écrire sa lettre modèle. Ou alors c'est un humain pas très compétent qui a juste googlé «quelle loi citer résiliation assurance», je ne sais pas. 🤷
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Et après de fort laborieuses vérifications, il semble que ChatGPT ait raison et que le modèle fourni par mon employeur était foireux (il invoquait un texte de loi pas du tout applicable ici, parce que relatif aux assurances auto et habitation, pas les mutuelles santé).
On dit (à raison) plein de mal des IA et de leur tendance à halluciner, mais j'ai fait relire par ChatGPT une lettre écrite (pour résilier un contrat de mutuelle santé) sur un modèle fourni par mon employeur, et il m'a signalé que la référence juridique fournie n'était pas bonne.
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(To be clear, this is an unusually large area for a municipality even by Chinese standards, and it is far from being entirely urban.)
#TIL that the municipality of Chóngqìng, China, has an area (82 403 km²) almost equal to that of the country of Austria (83 879 km²). 🤯␤␤It also has a far larger population (32M versus 9M for Austria) but that part doesn't really surprise me.
Billet d'humeur sur les mises à jour informatiques (des distributions Linux, en l'occurrence) qui ont pour effet principal de casser ou supprimer des choses que j'utilisais: madore.org/~david/weblog/…
RT @HumansNoContext: pic.x.com/TmpoPjtB2X
RT @pbeyssac: Un pas de plus vers une société à la chinoise, tracage numérique progressivement généralisé de notre activité en ligne, sous… x.com/Europarl_FR/st…
RT @austinhill: It simply amazes me that mechanized Lego courses aren’t mandatory in early STEM schooling. pic.x.com/9aSY0TrTKK
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@JacqBens @drhingram @guyrleech @DavidDeeble Happy Thanksgiving! And thank you for your kind words.
Un tout petit geste de gentillesse qu'on peut faire envers les pigeons des villes (qui ont qd même la vie dure) en cette saison, c'est d'éviter de leur faire peur, parce que chaque fois qu'ils s'enfuient en s'envolant, ils doivent consommer plein de calories dont ils ont besoin.
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@laurentbercot … if we are to make sense of what the US is doing. This in no way means that either one of Rubio and Vance is “good” or even “better” (from Ukraine's perspective), but the difference exists, and is important to any understanding of the situation (or geopolitics in general).
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@laurentbercot PS: I just stumbled upon the following example: the video youtube.com/watch?v=egSF6U… explains how Rubio and Vance have a very different perspective on the US role vis-à-vis Ukraine; so anyone who cares about this war should probably understand this fact, which matters a lot …
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@laurentbercot Admittedly, the fact that searching google.com/search?q=535.4… for various numerical approximations of e^(2π) returns pretty much only crank papers (e.g., results on viXra) does cast a shade of doubt on the importance of that number.␤␤BUT THEY LAUGHED AT GALILEO TOO! 😬
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Also, I could point out the fact that e^(2π) ≈ 535.49 is one of the determinations of 1^i, which is just another different, but perhaps pithier, way of saying the same (and makes you want to write e^(2πx) as “1^(i·x)”, which is wrong but fun).
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Also, I could point out the fact that e^(2π) ≈ 535.49 is one of the determinations of 1^i, which is just another different, but perhaps pithier, way of saying the same (and makes you want to write e^(2πx) as “1^(i·x)”, which is wrong but fun).
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To put it differently: if you take a fundamental domain of a complex exponential, it's a strip, and if you cut that strip into squares, each square is a factor e^(2π) ≈ 535.49 larger or smaller than the next.␤␤(E.g., a Mercator projection near the pole.)
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Basically, once you accept that the Fourier transform of f is fˆ(ξ) = ∫f(t)·e^(−2π·i·ξ·t)·dt (and that the natural unit of angles is the full turn, not the radian), you also accept that the Laplace transform is given by ∫f(t)·e^(−2π·s·t)·dt.
Probably unpopular opinion: I'm warming up to the idea that the best / most natural base for exponentials is neither 2 nor e (and certainly not 10), but rather e^(2π) ≈ 535.49.
It has come to my attention that not everyone is familiar with this masterpiece that is the song/clip ‘Amish Paradise’ by “Weird Al” Yankovic, so let me attempt to remedy this unfortunate state of affairs. youtube.com/watch?v=lOfZLb…
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So note that this is NOT the same as saying that the ECJ made same-sex marriage legal throughout the 🇪🇺, as some are surely going to claim (either to praise the decision or to scorn judicial overreach).␤␤But it is a hugely important ruling nonetheless.
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It's not quite so far-reaching as Obergefell v Hodges in the 🇺🇸. From the press release of the ECJ itself curia.europa.eu/jcms/jcms/p1_5… : “The Court emphasises, however, that that obligation does not require marriage between persons of the same sex to be introduced under domestic law.”
The ECJ “finds that refusing to recognise a marriage between two Union citizens, lawfully concluded in another Member State […] [on the ground that domestic law does not allow marriage between persons of the same sex], is contrary to EU law”. 🥳 x.com/EUCourtPress/s…
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I'd like to know how this particular experiment was conceived. 😆
IIUC, having a passenger dressed as batman causes other passengers to be more willing to give up their seats to a pregnant woman in the subway (in a statistically significant way). nature.com/articles/s4418…␤␤Pagnini &al, “Unexpected events and prosocial behavior: the Batman effect”
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(Je veux dire qu'elle a été modifiée trois fois, et que donc trois fois il a dû faire une annonce pour dire «finalement on dessert les gares suivantes».)
Je sens comme une pointe d'agacement dans la voix du conducteur du RER dans lequel je me trouve et qui nous annonce pour la troisième fois que la mission a été modifiée.
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There are various ways you can play Zork online. For example, take the `zork1.z3` file from the COMPILED/ dir in the Zork I code, then go to iplayif.com/api/sitegen and it will convert it to a playable HTML file (this is neat!).␤␤Or go to: archive.org/details/zork-t…
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(To be clear, the code was already available publicly since 2019. What has changed is that there is now an official license.)
For those who know what this is about: Microsoft made the source code to the games Zork I, II and III open source under the MIT license: opensource.microsoft.com/blog/2025/11/2…␤␤Actual code is here: github.com/historicalsour…
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Also, “we should ever conduct ourselves towards our enemy as if he were one day to be our friend” is a beautiful maxim.
The sartorial equivalent of Postel's principle (aka robustness principle for the Internet): “be conservative in what you send and liberal in what you accept”. en.wikipedia.org/wiki/Robustnes… x.com/dieworkwear/st…
RT @olesovhcom: Dans environ 6 mois, le prix de RAM et les disques NVME vont augmenter .. de beaucoup. ␤␤C'est lié à la demande AI: toutes… x.com/scaling01/stat…
pic.x.com/TzcDwdNZU1
Petit rant (pas trop interminable) sur les interfaces graphiques, censées simplifier la vie des gens, mais rendent en fait toute sorte d'automatisation quasiment impossible: madore.org/~david/weblog/…
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@ArthurB … I mean, it is logically possible that some of my students come to the math classes I teach because they want to learn about gay sex because they hate gay sex, but I think we can agree that this would be a little… bizarre. This is, in effect, what Ted Cruz is claiming to do.
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@ArthurB … Cruz seems so bent on believing that academics are biased in what they teach by their own beliefs that he thinks (or claims to think) that you would learn more from the course about the teacher's biases than about the subject matter, which is nuts. …
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@ArthurB … I mean, I fully agree with the “understand what you're fighting” or “know your enemies” principle, and the idea being expressed makes sense in general, but in this particular context it seems completely strange. … x.com/gro_tsen/statu… x.com/gro_tsen/statu…
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@ArthurB I guess they can, but attending a zoology class because the professor just happens to be communist and you want to understand communism would be… pretty weird, even for Ted Cruz. If you want to understand communism, you attend a course ON communism, not BY a communist. …
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@ArthurB No, the key point here isn't “Harvard”, it's “Law School” (which is where Ted Cruz went). Marxists don't teach (what they consider to be) the bourgeois legal system.
RT @MarkKersten: Three countries - the United States, Israel, and Argentina - vote against a UN General Assembly resolution aimed at preven…
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@laurentbercot Yeah, I really wish I could say that Quine's trick, or the Y combinator, or such, has a direct practical application, but I can't. My excuse for teaching this is I do think it offers an essential perspective on what recursion and functional programming are all about, however.
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Plain text version: gist.github.com/Gro-Tsen/c072e…
How to define recursive function calls in functional programming languages using Quine's trick (aka the ‘Y’ and ‘Z’ combinators): the same demo in OCaml (with recursive types), Python, and Scheme: pic.x.com/TMhh1DswWP
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(For those who missed the joke, see en.wikipedia.org/wiki/Survivors… esp. the first image.)
I guess this means we should reinforce North Ireland or something. x.com/amazingmap/sta…
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@monsieurpuyo Oui, complètement. Je n'ai pas d'image aussi jolie pour illustrer, mais je déteste le chaud au moins autant que le froid. xkcd.com/1916/
Are these communist professors in Harvard Law School in 1995 in the room with us now, Senator Cruz? x.com/tedcruz/status…
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@laurentbercot @Jilcaesel PS: regarding this 🔽, my own attempt madore.org/~david/weblog/… at defining how I see the left-right axis is that the values of the left are liberty, equality, fraternity & solidarity, those of the right are property, security, prosperity & responsibility. x.com/laurentbercot/…
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@laurentbercot @Jilcaesel … So those who disagree with the “canonical” positions of their side on this or that issue might be tempted to hide it for fear of anathema, and you get a self-reinforcement mechanism.
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@laurentbercot @Jilcaesel … so, yes, I agree that it exists and is very important, but to large extent I think it is the result of dangerous groupthink (on the right AND the left): if you start deviating from the canonical direction on the issues that have been grouped together, you can get cast away. …
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@laurentbercot @Jilcaesel … but their left-right axes might not, in fact, be the same, so the one-dimensionality is largely the effect of their own views.␤␤Second point is that there is a huge social pressure to conform to a pre-established left-right axis: …
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@laurentbercot @Jilcaesel One is that it reflects your own interests and beliefs about what is important. Someone who cares about fairness of wealth distribution, someone who cares about freedom of expression, and someone who cares about social issues might each agree that everything is left-right, …
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@laurentbercot @Jilcaesel [Typing in the car and thinking out loud, so this might not make a whole lot of sense.]␤␤The thing about one-dimensionality of the political spectrum is that it can have major confounding factors. I can think of two off the top of my head: …
Bon, j'en ai marre de l'hiver. C'est quand que c'est le printemps? x.com/gro_tsen/statu…
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@laurentbercot @Jilcaesel PS: Also, even insofar as there actually are 2 sides, the thing about centrism is that it is often politically expedient to CLAIM to be “centrist”, so it's very different to say that centrists are wrong than to say that people who CLAIM to be centrists are wrong.
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@laurentbercot @Jilcaesel … but even, other people can also be wrong about lots of things without being on the same “side” in a meaningful way (inside any parameter space, there are always more ways of being wrong than of being right).
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@laurentbercot @Jilcaesel … and makes them appear extraordinarily powerful and present everywhere, but there are all sorts of problems with considering “wrongness” to be a side of itself. Which is not to say that some groups can't be wrong about every non-trivial issue (e.g., actual nazis), …
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@laurentbercot @Jilcaesel … So how do I decide whether the same phenomenon is not happening on all sorts of other issues in which I don't happen to be similarly engaged myself? ❧ And you can see that defining “the other side” as “the side of wrongness” trivially makes them wrong about everything, …
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@laurentbercot @Jilcaesel As you know, during the covid-19 pandemic, I was suddenly lumped, by many people, as part of the “wrong side” (and did, indeed, find myself agreeing with people with whom I had very few commonalities on other issues). It was not a pleasant experience. …
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@laurentbercot @Jilcaesel My epistemological issue is whether this “side” actually exists as a side (meaning, among other things: do they consider themselves to be a common side?) or whether it is an a posteriori reconstruction based on the grouping together of people who are wrong on different issues.
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@laurentbercot @Jilcaesel Ah, sorry, I had never encountered the phrase “enlightened centrism” before, so I just took it for the combination of its constituent terms.
RT @bearstech: Ce mème vit sa propre vie... pic.x.com/2BIwvUSpV6
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@Moinsdeuxcat Cf. bsky.app/profile/did:pl… et bsky.app/profile/did:pl… — et a vu du second («j'ai argué̈»), je pense que tu te doutes que je n'ai aucun problème avec «nous haî̈mes».
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@laurentbercot @Jilcaesel I mean, between “the truth lies always in the middle” (the centrism fallacy) and “centrism is a mental disease” (the centrism-fallacy fallacy), there is room for a kind of middl… uh, never mind I said that. 😅
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@laurentbercot @Jilcaesel … There is simply universally applicable rule to detect correctness, certainly not one so trivial as “centrists are always wrong”. And you can say that this particular person said something egregiously stupid without trying to relate it to such a take.
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@laurentbercot @Jilcaesel For my part, I fully agree that I suffer from the “centrism fallacy” to some extent, and that I might be biased towards centrist takes. BUT to suggest that centrists are always so wrong that it's a kind of mental disease is a “centrism-fallacy (meta)fallacy” of kinds. …
Je parle un peu de physique des particules sur mon blog, avec le mystère de la formule de Koide (coincidence numérique ou signe de quelque chose d'intéressant? à vous de décider): madore.org/~david/weblog/…
This comic could turn out to be useful in many online discussions. savagechickens.com/2025/11/the-op… pic.x.com/NGEqzS6Ph7
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@JacqBens Now we just need to find some meaning for the mirrored exclamation mark. 😉
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@JacqBens Indeed⸮
“Earth is on fire” metaphor got a little out of hand at COP30: bbc.com/news/articles/…
RT @Jilcaesel: @BrunoDandolo La supercherie de prétendre que ちらみす est un mot italien qui désigne une spécialité italienne est éventée.␤http… x.com/kane/status/19…
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@JacqBens Ah, I see the confusion: there is indeed an “irony mark” that has been proposed which looks like a reversed question mark and would be perfect in your example, but it's reflected like ‘⸮’, not turned upside-down like Spanish ‘¿’. en.wikipedia.org/wiki/Irony_pun… 😜
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@RnaudBertrand Do you know if he tried suing French banks, and the 🇪🇺 branches of Visa and Mastercard, in France, for breach of contract, refusal to deal, and/or discrimination? If so, what did the French and European courts say about this? (I would imagine his fellow judges be outraged.)
RT @RnaudBertrand: In a normal world, this should be an immense scandal in Europe.␤␤Le Monde has a long article (lemonde.fr/international/…) d…
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Si vous ne vous habillez pas comme ça aujourd'hui, permettez-moi de vous dire que vous n'avez rien compris à la modernité: pic.x.com/YzeNkDWKZX
Si vous voulez une petite dose de rétrofuturisme, voici la France de 1970 et après, imaginée en 1965: youtube.com/watch?v=eRMuBU…
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Sources: Flammarion, bien sûr: “La Fin du monde” (1894), page 115, chapitre IV de la première partie gallica.bnf.fr/ark:/12148/bpt… et “Astronomie populaire” (1880), page 101 du tome 1, chapitre VII du livre I gallica.bnf.fr/ark:/12148/bpt…
Mood: pic.x.com/PrpHoPyf6S
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@antoineducros @pianocktailiste @informatheux … Il me semble que «il y a telle construction dont la définition technique est pénible mais dont ce qui m'intéresse est l'ensemble des propriétés suivantes» est la manière dont on travaille dans plein de domaine des maths.)
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@antoineducros @pianocktailiste @informatheux … (Et honnêtement, si l'attitude consistant à ne rien admettre est certainement louable sur son principe, quel mathématicien peut prétendre avoir connaissance d'une chaîne logique sans interruption entre les axiomes de ZFC et son théorème difficile préféré? …
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@antoineducros @pianocktailiste @informatheux Ben comme je dis, ça dépend du public visé. Mais en général, on peut faire un cours économique, un cours où tout est démontré, et un cours qui donne une bonne intuition, on peut même faire deux des trois, mais pas les trois à la fois. …
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@antoineducros @pianocktailiste Tout ça doit être expliqué dans le livre de Henri Cohen sur la théorie des nombres computationnelle, je pense.
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@antoineducros @pianocktailiste … Et l'opération fondamentale c'est d'augmenter la précision de l'encadrement, ce qui se fait avec des techniques numériques (méthode de Newton) et de vérifier qu'il n'y a qu'une seule racine dans un encadrement proposé.
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@antoineducros @pianocktailiste Un polynôme annulateur séparable (qui n'est pas forcément minimal, concrètement on factorise seulement quand nécessaire) + un encadrement (rationnel, disons) des parties réelle et imaginaire de la racine voulue, qui la rend unique dans l'encadrement. …
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@pianocktailiste @antoineducros A contrario, d'ailleurs, calculer des expressions en radicaux est super merdique. J'en avais sué pour calculer ces expressions de cos(2⁢π/11) et cos(2⁢π/13) utilisant uniquement les [déterminations principales de] racines k-ièmes: madore.org/~david/weblog/…
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@pianocktailiste @antoineducros (Je veux dire que trop de gens, ayant entendu cette histoire de non résolubilité en radicaux de l'équation générale du 5e degré, en concluent à tort que c'est plus difficile à manier informatiquement de telles équations, soit numériquement soit algébriquement… ce qui est faux.)
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@pianocktailiste @antoineducros D'ailleurs, le fait qu'on sache algorithmiquement faire des calculs ✵exacts✵ sur les algébriques (je veux dire, dans la clôture algébrique de ℚ dans ℂ, y compris des tests d'égalité et d'inégalité) me semble trop peu connu par rapport à cette histoire d'équations du 5e degré.
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@pianocktailiste @antoineducros Hum, du point de vue de la complexité algorithmique, calculer des racines n-ième n'a rien de plus simple que calculer des racines de polynômes (à racines simples) quelconques. Pour un humain avec un stylo c'est peut-être différent, certes.
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@pianocktailiste @informatheux @antoineducros … Je veux dire que je pense qu'on peut (selon le public!) prendre l'approche «admettons qu'il existe un truc appelé “groupe de Galois” vérifiant telles et telles propriétés, que je vais vous expliquer intuitivement, et on va voir ce qu'on peut l'utiliser pour faire».
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@pianocktailiste @informatheux @antoineducros … et @antoineducros faisait remarquer que c'est probablement plus difficile de prouver des choses avec ce point de vue, ce qui est sans doute vrai, tout sacrifice a un coût, mais peut-être qu'il vaut alors mieux renoncer à donner des preuves complètes. …
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@pianocktailiste @informatheux @antoineducros … S'agissant de la théorie de Galois, je pense que c'est plus intuitif de l'approcher initialement comme «symétries des racines d'équations polynomiales» que comme «automorphismes d'extensions de corps», …
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@pianocktailiste @informatheux @antoineducros … mais ce n'est pas la seule, et parfois ce n'est pas la meilleure (et ça dépend vraiment du public). On peut aussi, par exemple, multiplier les exemples, et on peut aussi renoncer à donner des démonstrations complètes mais des idées/intuitions de preuve. …
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@pianocktailiste @informatheux @antoineducros Disons que je crois que le message qu'@informatheux peut-être et moi sûrement essayons de faire passer, c'est qu'il y a plusieurs façons de simplifier un cours de maths trop difficile: diminuer la généralité et/ou le formalisme en est une, sûrement nécessaire dans bcp de cas, …
If the words from the image below were used in a post just above the image itself, then that post would be self-referential. pic.x.com/nuhmBKCWTU
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@VicP37508921 J'ai écrit quelques idées au détour d'autres billets ou ailleurs, mais rien de spécifique sur le sujet.␤␤Ici par exemple sur MathOverflow: mathoverflow.net/questions/4988…
¿Why haven't languages other than Spanish adopted this great convention of opening question and exclamation marks just like we open parentheses and quotes?␤␤(¡It's not like you need anyone's permission to use it! Nor does it risk confusing anyone.)
RT @Jilcaesel: “Bugger the sunk cost fallacy, we've given up too much.”
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@pianocktailiste @antoineducros … ce qui, pour le coup, permet effectivement d'alléger le formalisme, et/ou donner des intuitions de comment les choses fonctionnent, et ensuite montrer la théorie de Galois «en action» sur des problèmes concrets.
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@pianocktailiste @antoineducros … si le but est de faire «comprendre» à des étudiants comment «marche» la théorie de Galois, leur donner une preuve complète à partir de rien n'est pas forcément le meilleur but; je pense qu'il vaut mieux admettre certaines choses, …
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@pianocktailiste @antoineducros … Je veux dire qu'Antoine a raison: ce qu'on cherche à économiser en diminuant le formalisme ou la généralité, on le paie forcément quelque part après. CECI DIT, je pense que c'est ta contrainte qui est peut-être un peu bizarre: …
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@pianocktailiste @antoineducros La légende (rapportée par Proclus) veut qu'Euclide aurait répondu à Ptolémée Ier, qui lui avait demandé un moyen d'apprendre la géométrie sans payer le ticket d'entrée (c'est moi qui glose 😅), qu'«il n'y a pas de voie royale vers la géométrie». 😉 …
RT @SaarelaHC: Highland Cattle photo of the day pic.x.com/FzLXtNP9bX
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@antoineducros @pianocktailiste En fait, «plus simple» ne veut pas dire grand-chose dans l'absolu. Ça dépend énormément du public visé, au moins leur culture préalable, et souvent la disposition d'esprit de chacun. (C'est le problème de l'enseignement: de devoir parler à la fois à N personnes très différentes.)
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@Math4Rou @Jojo_le_poisson … Il y a aussi un effet de renforcement par le réseau, que je ne comprends pas bien. Mais tout ça est assez bien expliqué dans la vidéo que je cite ici: x.com/gro_tsen/statu…
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@Math4Rou @Jojo_le_poisson … Ici le problème est essentiellement que Musk veut absolument éviter une IA “woke” (🙄) donc il n'arrête pas de faire des ajustements pour essayer de rendre l'IA non-woke, pour qu'elle n'ait pas peur de choquer, etc., et sans rien contrôler. Forcément, ça donne MécaHitler. …
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@Math4Rou @Jojo_le_poisson Ce n'est pas une hallucination au sens usuel. Les hallucinations des IA, c'est quand elles n'ont pas d'infos sur un sujet et qu'elles extrapolent créativement. Sur l'holocauste, évidemment qu'elles ont toutes les infos possibles imaginables. Donc c'est différent. …
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@Jojo_le_poisson … l'autre est de faire du réentraînement: ça permet des modifications plus subtiles et plus indétectables, mais l'ennui c'est qu'on sait assez mal obtenir ce qu'on veut.␤␤Une explication assez bien faite du désastre précédent est là: youtube.com/watch?v=r_9wka…
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@Jojo_le_poisson Il y a deux types d'actions possibles: l'une est très facile et grossière, c'est de modifier le system prompt (ce qui est injecté au début de la conversation pour donner des instructions à l'IA); le problème, c'est que ça a tendance à backfire spectaculairement; …
RT @ChaireEtuParl: 🔴 Alerte publication‼️␤␤🔎Première chronique sur la vie du Parlement␤Une analyse de la vie parlementaire du 1er juillet a…
RT @haveigotnews: MI5 has warned of Chinese spies gathering intelligence on the British parliament, making them the only ones who know what…
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@ngspiensfr You're burning a straw man and you know it. Nobody seriously thinks it's impossible to write buggy code in Rust. The issue is whether it will happen less frequently enough for a net gain. I don't know, and I welcome studies on this, but the plural of “anecdote” isn't “data”.
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@pianocktailiste … Et donc ne pas parler de corps, d'extensions de corps, mais juste d'équations, et de racines de ces équations. Mais je pense que ça demande beaucoup de boulot quand même.
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@pianocktailiste Alors je pense qu'il faut présenter la théorie de Galois comme «symétries des racines», i.e., un élément du groupe de Galois de l'équation f(x)=0 est une permutation des racines qui préserve toutes les relations rationnelles entre elles. …
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Receipt in case the tweet is deleted: (Twitter won't let us post links to archive dot is 🙄, so I needed to make this into a QR-code). pic.x.com/4AFFSM24te
Just to make sure what is going on is on public record, here's Grok explicitly denying the (historically certain) fact that the gas chambers in Auschwitz were used for mass killings.␤␤[Tweet id: 1990496938417139943] pic.x.com/SdHjVfl8ad
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@pianocktailiste Il y a une formule générale, il n'y a juste pas de formule générale avec uniquement des racines k-ièmes (et les opérations rationnelles).␤␤Après, je ne sais pas ce que tu veux dire par «comment enseigner»: tu veux donner quoi, une idée? un énoncé précis? une preuve?
Petite réflexion sur la genèse des idées, et pourquoi mathématiciens et historiens des sciences pensent souvent les choses de manière très différente: madore.org/~david/weblog/…
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[The excerpt shown in the previous post is taken from Laurent Lafforgue, “Chirurgie des grassmanniennes” (2003), page iii.]
“Dear algebraic geometrist, can you explain to me the theorem of Thales?”␤␤“Very simple, dear: in the 7th century BCE, Thales of Miletus proved that configuration spaces of points in the projective plane are universal in the sense of Grothendieck's motives.” pic.x.com/g3HT5r0piR
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@pianocktailiste @random_poisson @EvarixGaulois Et racontée ici bsky.app/profile/gro-ts… avec une suite possible: ⬇️ pic.x.com/Bk6WtRZF0z
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@pianocktailiste @random_poisson @EvarixGaulois 🔽 x.com/gro_tsen/statu…
RT @JDHamkins: One of my graduate students asked a great question today: does Zermelo's proof of the well-order theorem from AC use the rep…
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@pianocktailiste @EvarixGaulois @random_poisson En fait, tu es dans le déni comme l'était mon papa. 😔␤␤Il faut faire le test ultime: si je te demande “où suis-je?”, que réponds-tu?
I asked a long sprawling question on MathOverflow on the relationship btw two flavors of reverse mathematics: one which weakens comprehension in classical logic, and one which works in intuitionistic logic but allows comprehension: why are they so similar? mathoverflow.net/questions/5040…
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@laurentbercot Hence “might”. If the hypothetical leftist doesn't think they are equally bad, then my point is already clear: I'm saying that even if some do think that they are equally bad, there are still important differences other than of moral judgment, and these differences matter.
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(By this I mean that nobody in early 1914 Europe imagined that, 4½ years later, the image conveyed by the word “war” would be so very different than what it was for them.)
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This observation is, of course, applicable to any historical context whatsoever: characters act without being cognizant of the consequences of their actions that we know, and this taints the way we judge their motivations. But this is particularly relevant for WW1.
A completely obvious point that I somehow hadn't really registered:␤␤‣ When we consider the causes of WW1 and which people or countries wanted to go to war, we need to keep in mind that “war”, to them, did not mean the same that, with ✵hindsight✵, we now know WW1 would be.
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@plumsirawit Hausdorff dimension makes perfect sense to compute here (but I don't really know how to do it in practice). Curvature doesn't, I think: it would end up being infinite everywhere.␤␤But I wanted a visual/intuitive answer, which you provided.
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@laurentbercot Concretely, a leftist might legitimately think that, in the last three US presidential election, the D candidate wasn't “better” than Trump, or that they shouldn't “pick sides”. But to say that the difference doesn't exist or doesn't matter is idiotic.
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@laurentbercot There are plenty of reasons to find differences among your enemies: they can be differences of power, of influence, of motivation, of psychology, of sociology, of whether you might turn them to your side, use them as temporary allies, etc. Ideology is only one factor.
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@laurentbercot But I never said you had to agree with anything, or find common ground!␤␤Look, consider a chess player, playing black: obviously ALL white pieces are the enemy, they have the EXACT same goal. But even then, the difference between the white queen and a white pawn matters hugely!
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@laurentbercot … But to say that ✱no✱ distinctions matter is, IMO, both intellectually unsound and tactically misguided (understanding your enemy always matters). I did say my test wasn't perfect, though, and I don't believe that you are conspiratorialist (even if I think you're wrong).
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@laurentbercot Ah but I'm not saying the labels they present THEMSELVES are relevant. The divisions that could matter (to you!) might be wholly orthogonal to the ideological ones (sociological or tactical, for example). Most people aren't ideologues anyway: they are opportunists. …
RT @mathladyhazel: The chemistry of Autumn leaf colors. pic.x.com/lKOj1z6myP
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Whereas anyone with a modicum of understanding of reality will realize that, in fact, there are internal divides inside any organization, and will take great care to understand their enemies' divisions so as to exploit them if possible (“divide ut regnes”).
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How it works is simple. Conspiratorialists will group their enemies in a single bunch (“them”), or will at best come up with bogus categories that all amount to the same. They don't really care because they really think of them as the arm of the One Conspiracy, whatever its name.
The following simple test, though by no means infallible, can be surprisingly effective in determining whether someone is a political crank or conspiratorialist:␤␤‣ Ask them to categorize their enemies, and describe the differences and disputes between them.␤␤That's all! ⤵️
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@JeanDellass Yes, I'm aware of the problem, and yes, this would be the right way to ask. But sadly, I had already posted the Möbius curve before I thought of asking the question, so the answerer pool was already tainted. x.com/gro_tsen/statu…
These very nice slides by Marie Farge on how researchers can regain control of publication have been brought to my attention: openscience.ens.fr/MARIE_FARGE/CO… — I think they're worth spreading more widely! pic.x.com/gP2vjPd7G2
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@YogiYogui No reason to be sorry! A negative result is also a result. x.com/gro_tsen/statu…
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@laurentbercot … So if the Möbius curve is somehow special, this begs for a number-theoretic explanation. If not, any features are harmonic-theoretic in nature. So, not the same kind of specialists to ask!
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@laurentbercot … But I can give you context: the Möbius curve was generated by (taking the Fourier transform of) a certain important number-theoretic function, the other four by using random coefficients with similar values and distributions. …
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@laurentbercot No, I don't want to bias the experiment by suggesting what I see, and which I may be projecting because I want to think this curve is special. If you say you don't see anything special offhand, that's a negative result. …
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‣ QUESTION: Do you think the Möbius curve stands out among the 5? Is there some visual property that makes it different from the 4 control curves? If I had shown all 5 to you, would you have said the Möbius one is somehow special? If so, how? Or is it just like the others?
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… And now consider these four other curves, which I will call the “control curves”: 🔽 … pic.x.com/y9dQtiqaQr
OK, I need an independent eye on this (especially from NON mathematicians). Please take a look at the overall appearance of this squiggly curve, which I will call the “Möbius curve”: 🔽 … pic.x.com/JEDRJNlAmN
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I posted a question on MathOverflow about this (with better quality graphs): mathoverflow.net/q/503986/17064
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If you want to hear what it sounds like, here it is at a 220Hz period (real part as the average between left and right ears, imaginary part as the half-difference). It's not super pleasant to listen to. pic.x.com/Xn3w70gAzZ
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To be clear, this is a plot of t ↦ ∑_n μ(n)/n exp(2·i·π·n·t).␤␤Its value at zero (so, ∑_n μ(n)/n) equals 0, sth already quite hard to prove (I think this is more or less equivalent to the Prime Number Theorem).␤␤Drawing this graph was inspired by this: x.com/gro_tsen/statu…
The Fourier transform of the sequence μ(n)/n, where μ is the Möbius function. Left, as a plot over time (over two periods, blue = real part, red = imaginary part), and right, as a parametric plot in the complex plane.␤␤Is there a number theorist around who might comment? pic.x.com/5mLysI58b0
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@tomgauld @GuardianBooks x.com/gro_tsen/statu…
I asked on Math StackExchange whether the sum of the μ(n)·q^n / n^s (for n=1,2,3…) admits a closed form expression (given that the sums of μ(n) / n^s and of q^n / n^s both do in a sense). math.stackexchange.com/q/5109103/84253
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It's true that Rogers covers some topics that aren't by Soare (like the hyperarithmetic hierarchy). For such things I would recommend turning to Odifreddi's “Classical Recursion Theory” (1989), which has the bonus of being available online: piergiorgioodifreddi.it/libri/matemati…
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In contrast, I find Rogers's famous classic “Theory of Recursive Functions and Effective Computability” (1967) absolutely atrocious (and horribly dated). Notations are abstruse, no intuition is ever given, and the numbering makes it impossible to navigate.
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Soare's 2016 book has several nice qualities. It manages to cover many important topics without being overly thick or dense. Its proofs are fairly readable, and the author makes a sincere effort to communicate some intuition. link.springer.com/book/10.1007/9…
If anyone wants to learn a broad overview of computability theory and Turing degrees, I recommend Soare's 2016 book “Turing Computability: Theory and Applications” (not to be confused with his 1987 book, “Recursively Enumerable Sets and Degrees”, which is much denser!).
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I suspect the above may be relevant for this problem 🔽 (or at least it has a similar flavor: very very roughly, you can communicate 𝐜 to someone who can compute the Turing jump while not communicating 𝐛 to someone who doesn't). x.com/gro_tsen/statu…
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Or, on the Turing degrees: if 𝐛>𝟎 and 𝐜 are two Turing degrees, there is 𝐚 such that 𝐚′ ≥ 𝐜 but 𝐚 ≱ 𝐛.␤␤Explanations here on MO by Noah Schweber: mathoverflow.net/a/503942/17064 (it follows from Cooper's jump inversion theorem)
Learned in passing on MathOverflow: if Y⊆ℕ is a noncomputable set and Z⊆ℕ is any set, then there exists X⊆ℕ such that the Turing jump X′ of X computes Z but X itself does not compute Y.␤␤This should be written black on white in textbooks!
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@JacqBens Let me guess: you must really dislike the music of Philip Glass, right? 😅
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@JacqBens I don't find it depressing, more like… contemplative.
Tentative (au succès mitigé) pour écrire un billet de blog pas interminable, en parlant du “réseau du mode par défaut” du cerveau, et pourquoi il faut peut-être accepter l'insomnie comme autre chose que du temps perdu: madore.org/~david/weblog/…
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(In fact, even ✺I✺ must have known it without realizing it because it's used as part of the soundtrack of incredibly many films, several of which I've seen.)
Apparently it's super famous and everyone probably knows it already, but I just learned about Max Richter's neoclassical musical piece “On the Nature of Daylight” (in ‘The Blue Notebooks’), and I think it's magnificent. youtube.com/watch?v=b_YHE4…
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Note: the oracle in question requires promise that at least one program does not halt (otherwise it kills you). But (exercise!) it actually doesn't change anything if we replace it by the slightly more lenient oracle which gives an arbitrary reply if the promise isn't fulfilled.
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This oracle can be called “LLPO” because it's basically the oracle version of the sequential LLPO principle (“given two binary sequences, if it is impossible that they both have a 1, then one of the two is the zero sequence”).␤␤And indeed, the topos it defines validates LLPO.
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The mathematically precise statement is that the topos of Lifschitz realizability is exactly the subtopos of the effective topos defined by the Lawvere-Tierney topology associated to the oracle in question (identified with a L-T topology as per Kihara's explanations).
Note to self: “Lifschitz realizability” seemed completely arcane to me until I understood that it corresponds to having access to the following oracle: I give the oracle two programs of which at least one does not halt, and the oracle returns one (of the two) that does not halt.
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(Ou peut-être qu'il allait lui couper les cheveux. Je n'ai pas regardé de trop près, je ne voulais pas faire le curieux. N'empêche que je crois que je n'avais jamais vu ça.)
Petite saynète de la vie quotidienne:␤␤Deux mecs (~20 ans, habillés en survêt) dans un square public à Paris. Sortent un fauteuil pliant, l'un s'assoit dessus, l'autre lui passe une serviette au cou, déballe du matériel de barbier de son sac, et commence à lui tailler la barbe.
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(“Éditions du Léopard masqué”, 90 rue Daguerre, Paris 14.)
Les titres ne sont pas exactement ceux que je me rappelais. 🤔 pic.x.com/vsxqpc3ohj
RT @2Philosophical_: Look, if we remove the slippery slope fallacy from the list of logical fallacies, then before you know it we’ll be rem… x.com/zymazza/status…
Coucher de soleil à Triffouilly-lès-Saclay pic.x.com/qGMGPe5Z6E
RT @pbeyssac: Un état impotent et désargenté est toujours tenté de violer notre vie privée pour se faciliter la vie. Redresser les finances… x.com/humanite_fr/st…
Le paquet promet que mes chips sont «défruitées de toute leur saveur». 😕 pic.x.com/Mnc8tQYx2h
Ikea octopus plushies (“BLÅVINGAD”). pic.x.com/cYQ87aMrNx
RT @vxunderground: I have never interacted with a single person amongst the sea of my 400,000 followers who has said, "I would like Windows… x.com/pavandavuluri/…
RT @haveigotnews: The UK has paused ‘intelligence sharing’ with the US following concerns over American military strikes against boats in t…
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@laurentbercot @ngspiensfr That is… a tolerable take. 😶
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@laurentbercot @Jilcaesel And passive aggressiveness is pretty much the definition of stoicism. existentialcomics.com/comic/130
Street Art, #Paris13 pic.x.com/HGBYP05wMl
City pigeons should be the emblems of stoicism.␤␤They have an absolutely shitty life, they basically eat garbage, many of them have deformed feet or other injuries, their life expectancy is abysmal, humans hate them and chase them away, BUT HAVE YOU EVER SEEN A PIGEON COMPLAIN?
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Confession: I think that “the natural numbers represent the forgetful functor from monoids to sets” is indeed a reasonable description of how we count repeatedly doing something (for any ‹something› we count n when doing ‹something›^n).
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(Warning: don't ask the same question to an n-category theorist, or they will start explaining that the integers were a mistake and we should be teaching about the sphere spectrum in kindergarten instead. mathoverflow.net/q/433863/17064 😁) pic.x.com/hxt9dj8w41
“Dear category theorist, can you explain to me what integers are?”␤␤“Very simple, dear: natural numbers are the object representing the forgetful functor from monoids to sets (and integers represent that from groups to sets). This is just how we learn to count in kindergarten.”
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@JacqBens … just so they could be used on Wikipedia to illustrate various biographies. And of course, since Souriau is over 100 now (if he's even still alive!), even pics taken when Wikipedia started still wouldn't show him in his prime.
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@JacqBens Wikipedia has fairly strict rules on the license of photos that can be used, so most official photos can't (except those produced by the US government because there's a great rule that makes them public domain); I have a friend who used to take lots of celebrity pics …
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@JacqBens … I do think there's something fairly profound about the meaning of mass hidden behind that jargon, but I don't understand it. However, I admit it does sound very cranky, and I got a lot of replies or QP on my tweet by cranks who wanted to promote their own idea of what mass is.
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@JacqBens The sentence, of course, is a very short summary of a good part of a (400+)-page book, it's condensed to make it sound abstruse, and I posted it half-jokingly (I got it from mathoverflow.net/a/51411/17064 and I was curious enough to try to make at least a little bit of sense of it). …
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@ngspiensfr OK, but can you at least explain what ✳︎sort✳︎ of changes you do? I can imagine that it's worth deciding when to wrap a line, or adding pairs of parentheses/braces, but that's not exactly part of the indentation rules. But changing the indentation itself, not really.
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@ngspiensfr Like, did you read the replies to the original post calling most indentation standards “mental disorders”?
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@ngspiensfr I will point out that you are the one who chose to feel targeted by a post against people who simultaneously like whitespace freedom (which you know is my case) and are anal about indentation rules. Are you seriously denying the existence of the latter?
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@ngspiensfr Care to show an example of a situation where there is enough flexibility and freedom in your preferred indentation convention so that it actually conveys some information that would be hindered if whitespace were not free?
I don't know who needs to hear this, but if “the other side are the baddies” is your excuse for twisting facts, laws or ethics, then not only is it a bad excuse, but you are undermining the very principles which are supposed to separate you from said baddies.
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@ngspiensfr But my point is mostly that it's hard to simultaneously argue that ① whitespace shouldn't matter so any language syntax where it does is brain-dead, and that ② there is one and only one right way to use whitespace and anyone not doing ✳︎exactly✳︎ this-or-that is an idiot.
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@ngspiensfr “Don't use stupid variable names” is ⓐ hard to formalize exactly, and ⓑ still leaves a lot of freedom to choose from. Indentation standards are algorithmic and seem to leave essentially zero freedom, so your comparison really doesn't work.
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@JacqBens PS: I would venture that this particular kind of madness is very French (along the lines of Poincaré, Bourbaki, etc.), not Canadian, and I'm not surprised that Souriau is French: fr.wikipedia.org/wiki/Jean-Mari…
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@JacqBens … For example, he makes a case that the difference btw the role of mass in classical mechanics and relativity (so, basically, “E=mc²”) is because of the mathematical fact the Galilean group has nonzero cohomology whereas the Poincaré group's is zero. I wish I understood why!
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@JacqBens … I'm convinced that Souriau has found a mathematically elegant, and possibly profound, way of describing physics (that sort of unifies and generalizes the Lagrangian and Hamiltonian formalisms), but I feel like I'm missing the central idea. …
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@JacqBens … But why this is a particularly relevant way of viewing mass (or why we care about momentum maps, or why they're defined the way they are) escapes me. en.wikipedia.org/wiki/Momentum_…
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@JacqBens It… really depends on what you mean by “understand”. I understand the mathematical concepts (Galilean group, cohomology class, moment map, symplectic manifold), and I can follow the (fairly easy, actually) computation that this equals mass in the usual sense. …
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Feel free to die on the “my whitespace is better than your whitespace” hill, but I'm not going to join you there.
Reactions to these indentation styles show two things about geeks/programmers:␤␤⁃ they like a language where whitespace is free, BUT␤␤⁃ they also want it known that if you use that freedom to do anything other than their exact favorite, you are an idiot.␤␤😂 x.com/fermatslibrary…
RT @alcidedessine: pic.x.com/3i757LiDfw
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(I thought ⓑ implied ⓐ but, as the trivial case of j=⊤ shows, this is not correct.) But whatever the exact condition, the moral is we can define the j-sheafification by a purely internal set construction, and this is the important message here. •9/(7+2)
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✱ Correction: my definition of a j-singleton above isn't quite right. I think it should be this: S⊆X is a j-singleton when␤ⓐ ∀x:X.(j(x∈S)⇒x∈S) [“j-closure”]␤ⓑ j(∃s:X.(∀x:X.(x∈S⇔x=s))) [as I had written]␤both hold. But now I need to check this more carefully. •8/(7+2)
I don't think this is the real reason for the term, but the joke (not mine) is too good not to be told. x.com/gro_tsen/statu…
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@AlvanArulandu You know the joke that the Higgs boson is also called the “God particle” because without it particles can't have mass? 😄
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@DjiBee Oui, ça aussi c'est scandaleux. Il devrait être obligatoire de fournir des PDF des notices de tous les produits, et de les garder en ligne pendant de nombreuses années.
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(Bon, remarquez, ceux qui sont carrément au niveau supérieur de cruauté malicieuse, c'est ceux qui donnent le même nom à deux modèles différents. J'espère qu'il y a un cercle de l'enfer spécialement pour ces gens.)
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Évidemment qu'on va perdre la notice sur laquelle cette info était écrite. Ou peut-être qu'on ne l'a jamais eue parce qu'on a acheté le truc d'occasion. Et maintenant on veut chercher de l'aide en ligne sur un produit dont on a juste la marque et même pas de référence précise. 😭
Les fabricants de produits (électroniques, électroménagers, etc.) qui n'écrivent pas la référence précise du modèle sur le produit lui-même… MAIS POURQUOI, GRANDS DIEUX, POURQUOI TANT DE HAINE? 😡
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@Blablablab1ub 🔽 x.com/gro_tsen/statu…
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@HieronymusT Sauf qu'en fait ce n'est pas l'OTAN qui est à l'origine de cet alphabet, mais l'Organisation de l'aviation civile internationale.␤␤Et “fox-trot” est un mot français, si, si.
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My father would have LOVED this. (Did I tell his favorite joke about the physicist in a balloon already?)␤␤And before you ask: yes, this is serious. It's a summary of §§ 12.121, 12.131 and 12.136 in J.-M. Souriau, “Structure of Dynamical Systems: A Symplectic View of Physics”.
“Dear mathematician, can you explain to me what mass is?”␤␤“Very simple, dear: the mass of a dynamical system is the cohomology class of the Galilean group representing lack of equivariance of the moment map on the symplectic manifold that is the phase space of the system.”
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@bangtandelrey_ Ah oui, c'est malin, ça! «‘A’ comme “Ali”», et la personne a l'autre bout saisit le signe «ʕ» ou «ʿ» parce que c'est la transcription de la consonne spirante pharyngale ʕayn qui commence le prénom ʕali en ʕarabe. 😅
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@kqcaral x.com/gro_tsen/statu…
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@robourobou La confirmation marche mal puisque (comme je fais toujours) j'ai posté la même chose sur Bluesky et Mastodon. Sauf que là-bas je n'ai pas eu les N relous pour faire savoir à tout le monde qu'ils s'en foutaient.
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@Scrf_88 x.com/gro_tsen/statu…
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@Mana_Mahad Mais quelle idée, pas du tout. x.com/gro_tsen/statu…
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@Cyrano3Bergerac C'est fou d'avoir autant besoin de le dire publiquement. Tu fais ça avec chaque tweet qui ne te passionne pas?
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@laurentbercot … But my main point is, neither of these very valid points is an excuse for piling on the “man in the middle” (who often turns out to be forced to do exactly that, parrot one side's argument to the other).
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@laurentbercot … and here again you know me well enough to know how much I care to point out 🔽 this very fact. But sometimes the truth IS somewhere in the middle, and it would be silly to claim the opposite. … x.com/gro_tsen/statu…
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@laurentbercot … I just don't allow the excuse “the other side is the baddies” to deflect blame that is deserved. The second is that truth can often lie not in the “middle” but in a completely different direction. This is also a very valid point, …
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@laurentbercot You make (at least) two claims here. The first is that there isn't always a middle ground to be found. This is quite correct but it's also a straw man. I never said the contrary. You know me well enough to know that I don't try to find compromise “at all cost”, …
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@UmmuLayan x.com/gro_tsen/statu…
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@KeMingRui57 x.com/gro_tsen/statu…
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@JeKalifa J'avoue que je ne m'y attendais pas. Grok a dû décider de montrer mon post a plein de gens, ou qqch comme ça.
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@Cravaterose x.com/gro_tsen/statu…
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@Cyrano3Bergerac x.com/gro_tsen/statu…
Mood: x.com/gro_tsen/statu…
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@canard_milliard Ben tant qu'on ne bosse pas dans l'armée ou quidlibet, on peut dire «Inde» pour «India» et «Novembre» pour «November», et admettons que pour M et X on utilise «Michel» et «Xavier». Je ne suis pas puriste, je dis juste que les prénoms chelous c'est chelou.
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@canard_milliard Ben on n'est pas obligé de prononcer à l'anglaise. Le génie de cet alphabet c'est justement qu'ils ont choisi les mots pour passer assez bien dans plusieurs langues, dont le français. Il n'y a guerre que India, Mike, November et Xray qui ne soient pas des mots français.
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@Jilcaesel @faelys_ Surtout que si on se met à faire ce genre de jeux, on ne sait plus si «soixante-douze» désigne 0x72 ou 0x6C (sans parler de 72 = 0x48) et le Club Contexte se frotte les mains.
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@Eve_Piper_ Everyone wants to dance with me. pic.x.com/PjjXNkAzQe
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👉 In a fight between two extremes, there are no points awarded for being the voice of temperance. You will just get insulted twice as much, and perhaps even more than that (because you will also be accused of the middle ground fallacy for not having a clear line).
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… something I was clearly not in the mood to get myself into.␤␤THEN I realized that the previous thought probably occurs to a lot of people, and that this is a major reason why public online political discussions are so polarized.
Seeing two people argue about a political question, I just realized the following obvious point:␤␤I was tempted to intervene and express a kind of middle ground position. Then I realized this would get me to argue with two (opposing) viewpoints at once, …
RT @gro_tsen: @Jilcaesel Et attention, l'hexadécimal B6 se prononce «dizante-seize» sauf chez les Belges où c'est «onzante-six».
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@Jilcaesel Et attention, l'hexadécimal B6 se prononce «dizante-seize» sauf chez les Belges où c'est «onzante-six».
RT @Emma___Palmer: Là j’ai senti une immense bouffée de fierté revancharde m’envahir et j’ai dit de ma plus belle voix "ah vous tombez bien…
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@ngspiensfr @Conscrit_Neuneu Et moi non plus‽
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@ngspiensfr @Conscrit_Neuneu Je pense qu'elle a disparu immédiatement.␤␤Je ne suis pas assez polémique pour une note de communauté. 😭
LA GLOIRE! x.com/Conscrit_Neune…
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Parce qu'un truc dont tout le monde se fout, par exemple, c'est qqch comme ça ⬇️ (j'aurai 0 réaction ici). Mais les réactions que j'ai eues à mon micro-rant sur l'alphabet phonétique montre que manifestement les gens ne s'en foutent PAS DU TOUT. 😂 x.com/gro_tsen/statu…
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@F4Y4FEL @AlexS75454006 Ah oui, pardon, Marcel c'est plutôt la génération d'avant, en fait, la génération silencieuse. meilleursprenoms.com/popularite-pre… Mais ceux qui sont encore en vie, c'est très majoritairement des boomers. pic.x.com/b2dSdV1Rt2
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… which locally has an element, ‣ and a j-sheaf is one in which every every such set has an element. ❧ To me this seems much more understandable than the definition typically given (⬇️) which involves extending j-dense subobjects. •7/7 pic.x.com/F4SJAe5mZV
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So if we think of j(p) as saying something like “p is locally true”, then: ‣ a j-separated set is one in which two elements that are locally equal are indeed equal, ‣ a j-singleton in a j-separated set is a subset whose elements are all equal (think “partial element”), … •6/7
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A j-sheaf is always j-separated; and if X is already j-separated, then every j-singleton is subterminal (this means all its elements are equal), and conversely, a subterminal subset is a j-singleton (resp. a singleton) iff it is j-inhabited (resp. inhabited). •5/7
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… here, by “j-singleton” in X I mean a subset S⊆X such that j(∃s:X. (∀x:X. (x∈S ⇔ x=s))) (without the initial j, of course, this is just a singleton). And in general, the set of j-singletons in X is a j-sheaf called the “j-sheafification” of X. •4/7
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Then a “j-separated” set X is one which satisfies ∀x,y:X. (j(x=y) ⇒ x=y); and in general “j(x=y)” defines an equivalence relation on any X, the quotient by which is j-separated. As for a “j-sheaf”, it is one for which every j-singleton is just a singleton: … •3/7
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I'll try to post some details later, but assume j:Ω→Ω is a Lawvere-Tierney topology (with Ω the set of truth values), meaning it satisfies ⓐ j(p₁∧p₂) = j(p₁)∧j(p₂), ⓑ p ≤ j(p), and ⓒ j(j(p)) ≤ j(p) (so, in fact, j(j(p))=j(p)) — think of it as a modal operator. •2/7
I thought the notion of “sheaf for a Lawvere-Tierney topology” was a very complicated one, but I realized it's actually not so complicated, and it can be defined completely internally (i.e., you don't need to know what a topos is, just how constructive math works). •1/7
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Mais à part ça, je suis curieux de savoir comment plein de gens sont tombés sur mon post, parce que normalement personne ne réagit à ce genre de râlerie, et je ne vois pas qu'un gros compte l'ait retweeté. C'est Grok qui a décidé qu'il fallait montrer? 😅 x.com/gro_tsen/statu…
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@F4Y4FEL @AlexS75454006 Boomer à seulement deux ans, c'est vraiment terrible! 😄
Les gens qui repostent un truc en même temps qu'ils écrivent «je m'en fous», ils ont l'air de ne pas comprendre que l'existence même de leur post contredit le message de leur post. x.com/lecrivaillon/s…
RT @YalkunUluyol: The Chinese government reached around the globe to shut down a film festival in New York City. This latest act of transna…
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@P5Lawrence @npopravka (Une question plus intéressante, c'est comment on nomme les caractères ASCII chelous comme ‘#’, ‘_’ et compagnie. Là aussi, chacun a cinquante noms différents et parfois très confusants.)
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@P5Lawrence @npopravka Ben «echo accent aigu», simplement (et si on veut dire qu'il n'y a pas d'accent, «echo sans accent»). Le but est de faire clair, pas de faire vite. Mais en général c'est utilisé pour dicter un truc comme une URL ou adresse mail, donc il n'y a pas d'accent en fait.
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@AlexS75454006 Bien tenté, mais s'il y a un truc de boomer, c'est justement l'alphabet avec les prénoms: fr.wikipedia.org/wiki/Alphabet_… — il a cessé d'être recommandé dans les années '80, et plus personne ne s'appelle Émile ou Marcel.
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@Robe_0000FF Justement, il est spécialement fait pour marcher dans plusieurs langues, et quasiment tous les mots existent en français tels quels… OK, si on veut dire «Inde», «Michel» et «Xavier» au lieu de «India», «Mike» et «Xray», mais tout le reste marche.
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@Jilcaesel Certes, mais mon point c'est qu'en fait les prénoms souvent ils n'arrivent pas à les trouver non plus, et ils feraient mieux de faire l'effort d'apprendre ce truc (ou ouvrir Wikipédia s'ils ont un ordi devant eux).
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@Jilcaesel 😂
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Et évidemment les gens qui font ça sont en fait incapables de trouver un prénom avec la bonne lettre, ou ils ne réfléchissent pas au fait que c'est ambigu («K comme Karine, enfin, Karine avec un K», bravo t'es un génie).
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Genre, on a inventé un alphabet spécialement pour rendre tous les termes bien distincts et pour fonctionner correctement dans plein de langues, au moins 3 organisations internationales ont planché dessus, mais non, flemme de l'apprendre, on va improviser avec des prénoms chelous.
Micro-trucs qui m'exaspèrent, ép. 20251108: les gens qui essaient d'épeler un mot avec des prénoms («F comme Fabrice, U comme Ursule, C comme Charles, K comme Kevin») au lieu d'utiliser l'alphabet JUSTEMENT PRÉVU POUR ÇA («Foxtrot Uniform Charlie Kilo»). fr.wikipedia.org/wiki/Alphabet_…
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@Janjean15 Indeed. But generally one tends to compare less famous people with more famous ones rather than the other way around, and in this case I meant that who is the more famous very much depends on whom you ask.
One of my mild OCDs is that I really hate writing on both sides of a sheet of paper.␤␤Except for scribblings that I'm going to throw away almost immediately, I feel compelled to use only one side (whether it's on notebooks, notepads, or loose sheets of paper).
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‣ Second, I'm pretty sure that some unnamed protobacterium made that discovery some ~4 billion years before Crick, Watson, Franklin, or any eukaryote were even around. 😄
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(But it is also not correct to say Franklin had everything worked out and Crick & Watson simply stole her work. As usual in the history of ideas, things are complicated: see threadreaderapp.com/thread/1650877… (= x.com/matthewcobb/st… ) and nature.com/articles/d4158… for detailed account.)
To those who describe Crick and Watson as discoverers of the DNA double helix structure, I'd like to remind:␤␤‣ First, Rosalind Franklin discovered it before them, but they failed to give her and her students proper credit, and Watson later disparaged Franklin's character. …
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@hanuljeon95 PPS: here's a direct proof given mutuals on the Good Place: bsky.app/profile/jeanas… pic.x.com/mTIQT9Qj07
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@hanuljeon95 PS: you may prefer to follow me elsewhere: x.com/gro_tsen/statu…
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@hanuljeon95 …␤␤∀q:Ω. ((((∃r:Ω. ((r∨¬r)⇒q))⇒q) ∧ (p⇒q)) ⇒ q)␤␤should just boil down to “¬¬p”. (At least for the internal logic of a topos: it's possible that there's a subtlety here, but I don't think so.)␤␤But looking at it, it's not super obvious (I didn't think too much, though.)
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@hanuljeon95 …␤␤p ↦ ∀q:Ω. ((((∃x:X. (x∈E ⇒ q)) ⇒ q) ∧ (p⇒q)) ⇒ q)␤␤Now we know that the smallest topology making the subobject 2 := {p:Ω | p∨¬p} dense in Ω is the ¬¬ topology (p ↦ ¬¬p), and if we apply the above formula it tells us that …
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@hanuljeon95 There's a folklore result (see mathoverflow.net/q/484068/17064 for proof+reference) that says that, in a topos, the smallest L-T topology j:Ω→Ω making a subobject E ↪︎ X dense (viꝫ. ∀x:X.(j(x∈E))) is given by the formula: …
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And I wonder if we can simplify␤␤∀q:Ω. ((((∃r:Ω. ((¬¬r⇒r) ∧ ((r∨¬r)⇒q)))⇒q) ∧ (p⇒q)) ⇒ q)
So in principle the (intuitionistic logic) formula␤␤∀q:Ω. ((((∃r:Ω. ((r∨¬r)⇒q))⇒q) ∧ (p⇒q)) ⇒ q)␤␤should be simplifiable down to just␤␤¬¬p␤␤— but I have to admit this isn't terribly clear. 🤔
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@ZeitblomS Super! Merci pour les liens.
Tiens, le premier ministre suédois Ulf Kristersson ressemble exactement à Bruno Retailleau (ou vice versa), physiquement et pas juste politiquement.
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Alors oui, on peut demander de l'aide à un vendeur, mais je n'aime pas ça, par timidité et parce que ça fait pression pour acheter après. Surtout si je cherche N titres.␤␤Pourquoi ils ne mettent pas juste des outils de recherche de leur inventaire, qui doit bien être informatisé?
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Le pire c'est sans doute les BD. Le classement n'a aucune logique, parfois c'est par titre, parfois par auteur (scénariste? dessinateur? comment savoir?), parfois c'est mélangé, parfois c'est par genre, et on ne sait pas dans quel genre est ce qu'on cherche (c'est quoi, «indé»?).
J'aime bien acheter des livres dans des vraies librairies plutôt que passer commande en ligne, mais il faut avouer que si on cherche un titre précis (p.opp. à juste feuilleter au pif), c'est merdique. On ne sait jamais comment les choses seront rangées.
Question pour les Belges et les Suisses: est-ce que quand vous êtes en France et que vous parlez à des Français vous vous adaptez à la façon complètement stupide dont les Français disons les nombres entre 70 et 99? reddit.com/r/French/comme…
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I even have a (circa 2010, I think) official plushie of the former Mozilla mascot. Look how sad and confused it looks at having been abandoned by its former owners: pic.x.com/NlMt03QYT9
Mozilla is trying to rewrite history, but those of us old enough to remember the 1990's know that they once had a LIZARD (green then red) as a mascot, whom they dumped unceremoniously in favor of their newly adopted red panda/fox. pic.x.com/OwmxfgRqyg x.com/nixcraft/statu…
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En gros, ça parle de ça: x.com/gro_tsen/statu…
Un billet de blog pour parler de façon un peu plus systématique des questions que j'ai évoquées dans quelques fils ici: madore.org/~david/weblog/… (je commence par une devinette, puis j'évoque une notion de «degré de co-Turing» duale de celle des degrés de Turing).
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@laurentbercot … It's a bit annoying to formalize, but the idea is you [Arthur] put your questions to a wise ally [Nimue] who answers yes/no and then an adversary [Merlin] converts this answer to pairs of Turing machines. Arthur and Nimue agree on a strategy beforehand, but can't communicate.
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@laurentbercot Just to be clear, though: the rules don't allow you to question the oracle's present or future answers (i.e., you can't ask “will your answer to this question be two machines which either both halt or both don't?” as this would spell instant paradox). …
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On dira tout ce qu'on veut, mais le futur de quand j'étais petit, il était mieux que le présent (ou même le futur) de maintenant: x.com/gro_tsen/statu…
Si le rétrofuturisme de la France des années 1970 et 1980 et/ou le personnage de Valéry Giscard d'Estaing vous donne une 🍆, voici exactement le clip qu'il vous faut: youtube.com/watch?v=KKhnDz…
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@laurentbercot I've tried various approaches, and I haven't managed to do anything, but feel free to try. (It's quite possible that my knowledge of certain topics biases my way of thinking and that there is a very simple solution.)
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But (back to the original form) I have no idea how to approach this riddle. I don't even know what answer I expect. I've been pulling my hair out, but I can't imagine either a strategy to gain information from the oracle nor a strategy for the oracle to withhold it. 😖
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Of course the fact that the halting problem is undecidable is crucial here; but alone this does not solve the problem, because if the oracle gave you a halting machine to say “yes” and a non-halting one to say “no”, you could easily obtain the answers you want (exercise: how?).
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[If you think my description above is too vague, here 🔽 is a mathematically precise version. The case discussed above is, as suggested by W. Sawin, when P the set of pairs of Turing machines which either both halt or both don't, and Q is its complement.] x.com/gro_tsen/statu… x.com/gro_tsen/statu…
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… And the oracle wants to prevent you from gaining any useful information from your questions.␤␤👉 Can you ask questions in a smart way to (computably) gain some useful knowledge from this oracle? Or can the oracle prevent you from doing this?
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… instead of answering “yes” or “no”, the oracle will present to you (each time you ask a question) two Turing machines: for a “yes” answer, one of the two machines halts and the other doesn't, whereas for a “no” they either both halt or both don't. …
So, one of the math questions I'm currently obsessing about is this deceptively simple one:␤␤‣ Imagine you have access to an omniscient oracle which can access an unlimited number of yes/no question. But there's a catch (of course): …
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@ngspiensfr @laurentbercot Je connaissais des éditions en VO mais pas aussi nombreuses et pas en VF. On devrait peut-être en faire une copie de sauvegarde dans un /books près de chez nous?
Ce titre. 😬 x.com/le_Parisien/st…
RT @rekdt: Tapping the sign again pic.x.com/S0P5urRDFj x.com/bleepincompute…
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… The title card “There is no Hyde” isn't ideal, however: to paraphrase the very relevant movie ‘Primal Fear’, I think the point isn't that there is no Hyde — it is, rather, that there is no Jekyll.
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… Rather, Henry Jekyll uses the fact that people can't recognize him when he's transformed into Edward Hyde to allow himself to let go of his social inhibitions. But there is no mental transformation, any more than wearing a different costume would induce. …
This video youtube.com/watch?v=uZqm6m… makes a good point: most people seem convinced that the transformation of Dr. Jekyll into Mr. Hyde is a mental as well as physical transformation, but the novella doesn't say this! There is no “split personality”. …
Incidental consequence: for any T-degree 𝐚 and 𝐛>𝟎, there are T-degrees 𝐜,𝐝₀,𝐝₁ such that:␤⁃ 𝐝₀ ∧ 𝐝₁ = 𝟎 (i.e., they form a minimal pair),␤⁃ 𝐜 ∨ 𝐝₀ ≥ 𝐚 and 𝐜 ∨ 𝐝₁ ≥ 𝐚␤⁃ 𝐜 ≱ 𝐛,␤which is surprising if you think they look like a distributive lattice. x.com/gro_tsen/statu…
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Update: I edited the question to post the proof of a partial result: for any Turing degrees 𝐚 and 𝐛>𝟎, there exists a set of degree ≱𝐛 that can successfully encrypt every set of degree ≤𝐚.
Might be a good time to recommend this documentary: 🔽 x.com/gro_tsen/statu…
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@pianocktailiste Je m'inspire du fait que souvent, en séminaire, la partie la plus intéressante est quand l'orateur rappelle les choses «bien connues» avant de parler de ses propres contributions. 😁␤␤(Et exposer comme ça m'aide à éclaircir mes propres idées.)
RT @EuropeanPirates: Where responsibility lies, lies our future.␤␤european-pirateparty.eu/when-digital-s…
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A history of the White House (the building!) and what its various extensions and renovations reveal about the extension of presidential power in the United States: youtube.com/watch?v=32G68F…
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It's inspired by this previous question, but it's different: x.com/gro_tsen/statu…
I asked a question on MathOverflow about whether some sets of integers can be used to “encrypt” another set while keeping the Turing degree of the encryption arbitrarily low. mathoverflow.net/q/503435/17064␤␤(This may turn out to be utterly stupid.)
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@Sotorumuro To be clearer, say that n is (10-) exponentiable if the above holds. Then ⓐ 0 is trivially exponentiable, and ⓑ if n is, then n+1 is; so in usual arithmetic, ⓒ every n is exponentiable (by induction on n). Ultrafinitists accept ⓐ and ⓑ but typically not ⓒ.
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@Sotorumuro Even more accurately, to say that “10^n exists” means there exists a finite sequence of length n with first term 10 and each term 10 times the previous one. In usual systems of arithmetic this is, of course, a very easy theorem. But ultrafinitists reject unrestricted induction.
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@Sotorumuro It's an abuse of language: any number exists, of course: the issue is whether “10^(10^100)” or such does, indeed, denote a number (or whether it's a meaningless expression such as 1/0).
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… so when we build a larger computer, ultrafinitists should, if not spend time probing for them, at least be excited about discovery of new numbers (“we confirmed 2^n exists for n=2^85” or so) like chemists are discovered about the discovery of new elements.␤␤Why aren't they?
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… So IIUC, ultrafinitists mostly accept the existence of 10¹⁰⁰ (that we can easily handle on a computer), but they doubt that of 10^(10¹⁰⁰) (which we can't). However, the construction of larger computers should let us test the existence (in their sense) of larger numbers, …
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… to write down a proof (in a system of bounded arithmetic) which basically consists of saying “2 exists, 2×2 exists, 2×2×2 exists…” through n steps (their gripe isn't that the proof is hard, but if n is large-ish, it's not because n exists that you can actually DO it). …
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IIUC (not sure!), mainstream ultrafinitists accept the totality of multiplication on the natural numbers (“if m and n exist, then m×n exists”), but typically not with that of exponentiation (“if n exists, then 2^n exists”): to convince them of the existence of 2^n you need …
Here's one reason I have a hard time taking ultrafinitism seriously:␤␤If ultrafinitists really believed what they say, they should get excited about the discovery of ever larger numbers. They should consider searching for evidence of them a valuable goal. Yet they don't. Why? 🤔 x.com/skdh/status/19…
RT @jothwip: pic.x.com/8TBh9Z9j1k x.com/EPM106/status/…
Mon poussinet a compris comment calculer un TAEG, donc maintenant il s'amuse à traquer les offres frauduleuses. x.com/Conscrit_Neune…
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@laurentbercot (C'est à 15′23″ dans le documentaire.)␤␤Et ils ajoutent (19′45″) que ça avait surpris et choqué de représenter la Liberté sous la forme d'une «poissarde» (je ne connaissais pas ce mot, d'ailleurs).
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@laurentbercot C'est dit très clairement par un des intervenants du documentaire qu'elle a du poil sous le bras.
Documentaire très intéressant sur le site d'Arte sur le tableau “La Liberté guidant le peuple” de Delacroix, son contexte, sa composition et son histoire: arte.tv/fr/videos/1194… (ce sera diffusé à la télé le 2 novembre)
RT @Anthony_Bonato: One sure way to scare people this Halloween pic.x.com/MgOSwSvhSZ
I really wonder what it's like, not being a royal prince, and having to wear a surname like the plebs, instead of being Prince Firstname or The Duke of Someplace.␤␤If only there were other people in this situation to help me explain what it's like, I could relate. Know anyone?
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Note: I'm not saying it would be a good idea, or that I'd want that, I'm just saying I'm surprised it doesn't exist.␤␤Is it because the technology to do this doesn't exist, or is it because the economics doesn't work out?
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Note: I'm not saying music-generating AIs don't exist. I know they do. But AFAIK, there's no public Web site where you type “a piano sonata in the style of Beethoven, quoting Elgar's ‘Pomp and Circumstance’ marches in every movement” and you get a shitty mp3 to download.
How come is it that we hear a ❉lot❉ about text-generating AIs (LLMs) and image/video-generating AIs, but almost never about music-generating AIs, even though many people consume a lot of music, perhaps more than any other form of art?
The Internet of Things: x.com/gro_tsen/statu…
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I also love the “The ethical conflict is just so basic and fundamental, you don't need a law professor to explain it” quote. 🤣 x.com/gro_tsen/statu…
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… And I also just love the candor he displays (at 56″ into this video) about the whole thing, how he finds it so funny to be both parties and judge at the same time: youtube.com/watch?v=m5dhJ2…
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… And IIUC, it's in the “certainly illegal, but nobody can do anything about it” category, which is also a genius concept in and of itself. youtube.com/watch?v=gFQWHF… …
Trump is so cartoonishly corrupt it becomes sort of funny, but you have to admit, the idea of claiming the federal government (which he now heads) owes him damages, and then ordering his underlings to “settle” the case so he gets the money is pure genius in its simplicity. …
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@laurentbercot @ngspiensfr Et par ailleurs, la transformation que @ngspiensfr a faite est un exemple du phénomène appelé “heavy NP shift” (ou “end-weight principle”) en linguistique. en.wikipedia.org/wiki/Heavy_NP_… Donc oui, c'est standard et documenté comme tendance.
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@JDHamkins Ahem. x.com/gro_tsen/statu…
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A 3-part documentary by (French-German TV channel) Arte on the US geopolitical influence in Latin America: p1 (“Coups”) youtube.com/watch?v=xcoeP3… ❧ p2 (“Wars”) youtube.com/watch?v=k-FcXW… ❧ p3 (“Chaos”) youtube.com/watch?v=yFVR5b…␤␤Also at: arte.tv/fr/videos/RC-0… youtube.com/watch?v=xcoeP3…
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I asked a long question on MathOverflow about this game, with detailed explanations and some remarks and comments: mathoverflow.net/q/503195/17064
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@monsieurpuyo La baie (“poivre”) de Sichuan est le même genre, et peut-être même la même espèce (c'est ambigu) que la baie de Timut. Donc oui.
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Et en plus, le goût de ce machin reste TRÈS longtemps dans la bouche. 😣
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Je ne dis pas que la baie de Timut est dégueulasse, mais ça a à peu près autant de rapport avec le poivre que le sucre en poudre avec la poudre de piment: si on remplace l'un par l'autre, on va être surpris.␤␤Donc je conchie les gens qui vendent ça sous le nom de «poivre». 😡
Note to self: ce qui est parfois vendu comme «poivre de Timut», c'est de la BAIE de Timut, Zanthoxylum armatum, qui n'a RIEN À VOIR avec du poivre (Piper nigrum), et malgré une vague ressemblance, n'en a PAS DU TOUT le goût.␤␤Et si on remplace l'un par l'autre, c'est dégueu. 🤮
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@laurentbercot Allow me to submit this shameless self-plug: madore.org/~david/weblog/…
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@drmtgr Ben ce que j'essaie de dire, c'est justement qu'avoir du temps entre le lever du soleil et le début de la journée de travail, c'est mauvais parce que c'est du soleil perdu. Les gens profitent de leurs loisirs APRÈS le travail, pas avant: ce n'est pas symétrique.
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For example, I don't like it when people act like idiots, but I also think it shouldn't be forbidden.
One sign that someone isn't a complete idiot is when they manage not to confuse:␤␤⁃ [I think] X is forbidden,␤␤⁃ [I think] X should be forbidden,␤␤⁃ [I think] you should not do X,␤␤⁃ I don't like it when you do X.
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Réponse, donc: d'après clamart.fr/fr/actualites/… cette “tour carrée” ou “tour Duffaut” de Clamart est à l'origine un point géodésique, mais elle a un certain nombre de bizarreries, comme celle d'être ornée du buste d'un personnage entièrement fictif (“Elmer Dwight Edouard”).
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@ngspiensfr @laurentbercot Et la justification utilitariste sommaire, c'est que si la personne i aime qu'un certain paramètre X prenne la valeur x_i et que son utilité est a−c·(X−x_i)² (avec a et c>0 des constantes) alors l'optimum d'utilité globale est de mettre X à la moyenne des x_i.
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@drmtgr Je ne vois vraiment pas l'importance que ça a qu'on soit sur UTC+1 en commençant la journée de travail à 8h (disons), ou sur UTC en la commençant à 7h (disons).
C'est quoi cette tour très sophistiquée rue de Meudon à Clamart? google.com/maps/@48.80103… pic.x.com/XGJFG4uK85
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Et ce n'est pas symétrique lever/coucher parce que nos journées ne sont pas symétriques. On fait généralement boulot d'abord, loisirs après. Donc aligner le début avec le lever du soleil fait sens.
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‣ Or on aime bien commencer la journée de boulot EN GROS au lever du soleil. Et on aime qu'elle soit à heure civile fixe.␤␤‣ DONC il faut changer le décalage de l'heure civile par rapport à l'heure solaire, i.e., changer l'heure.␤␤…
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‣ FAIT ASTRONOMIQUE: en France, l'heure solaire de lever du soleil varie beaucoup auc ours de l'année (en gros: 8h solaire au solstice d'été, 4h solaire au solstice d'hiver).␤␤…
Plein de gens semblent ne pas comprendre pourquoi on change d'heure. Oui, à l'origine c'était une question d'économie d'énergie, mais maintenant c'est plus une question d'organisation sociale du temps.␤␤Je vous la fais en 3 points faciles: …
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A nice introduction to the Standard Model of particle physics (and some history thereof), which should be understandable by a fairly general audience; by John C. Baez ([at]johncarlosbaez[at]mathstodon[dot]xyz on the Fediverse): youtube.com/watch?v=0yjxqM…
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… Arthur seeing this chooses to either make a guess or continue the game (then Nimue again picks “𝙿” or “𝚀” and so on; note: b is only chosen once by Merlin). Importantly, Arthur must follow a ❋computable❋ strategy.␤␤⇒ For which P,Q do Arthur+Nimue have a winning strategy?
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… directly to Arthur except insofar as they agreed a strategy in advance. Nimue can only choose either “𝙿” or “𝚀”, pass this to Merlin, who then chooses an element of a subset P or Q ⊆ ℕ (both P,Q⊆ℕ fixed in advanced and known to the players) that gets shown to Arthur. …
Now thinking about the following math game:␤␤‣ 3 players. “Arthur” & “Nimue” are allied against “Merlin”. Merlin first chooses a bit b∈{0,1} and shows it to Nimue (not Arthur). Arthur's goal is to guess b, and Nimue (knowing b) tries to help him guess. But Nimue can't speak …
RT @tomgauld: My cartoon for this week’s @newscientist pic.x.com/QvgOONi4it
RT @JeremiahDJohns: Every startup now is like "We found a cool way to monetize undermining the social contract!" x.com/nearcyan/statu…
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@JeanDellass Le personnage joué par Jean Rochefort dans le (par ailleurs excellent) film “Ridicule” de Patrice Leconte est justement obsédé par l'idée de classifier les formes d'humour, le calembour étant la plus méprisée à la cour. pic.x.com/IDobZv7GJJ
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@JeanDellass Elle apparaît déjà au moins chez Prévert (“La crosse en l'air”, in: “Paroles” (1946): «au balcon sérieux comme un pape paraît le pape entouré de ses sous-papes»).
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Bref, se balader à Plaisir donne un peu la sensation d'être dans cette note de Boulet où les coiffeurs ne seraient pas les seuls commerces à faire des jeux de mots nazes dans leur nom: bouletcorp.com/notes/2009/09/…
Hier, @Conscrit_Neuneu et moi nous sommes baladés à Plaisir (Yvelines), et il y a partout exactement les jeux de mots sur le nom de la ville que vous pouvez imaginer.␤␤(P.ex., la mairie a fait des affiches vantant son action intitulées «faire Plaisir».)
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@JacqBens (Admittedly, I have no idea what four-element-chemists — if that is even a meaningful phrase — thought about boiling water: did they think it reacted with air? fire? that it remained water and just changed form? something else entirely? I don't know.)
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@JacqBens You might be able to make a battery by putting some lemon-soaked tissue between zinc and copper plates (assuming zinc is allowed 😅). But I'm not sure they'd necessarily be convinced: they might think it's something similar to making water boil.
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[ Relevant xkcd: xkcd.com/965/ — and Oglaf: oglaf.com/matter/ ]
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… “Promethium”? “Yttrium AND ytterbium”? “Ruthenium”? “Thallium AND thulium”? “Lutethium”? “Gadolinium”? “Praseodymium”? All of these things are elemental and Water isn't? You MUST be pulling my leg! (Also, how am I supposed to conjure an elemental of these things?)
Imagine travelling back in time to when people thought the four elements where Earth, Water, Air and Fire, and trying to explain that not only are none of these actually elements, but that there are >100, most of which they have never seen or heard about in any form. 😅 …
Wait, there's a book called “Shady Characters: The Secret Life of Punctuation, Symbols & Other Typographical Marks” (by Keith Houston) entirely devoted to telling the story of typographical symbols? Shut up and take my money! shadycharacters.co.uk/books/
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@JacqBens C'était l'idée de la magistrature exceptionnelle de «dictateur» à Rome, mais ils étaient élus pour un temps très court avec une mission étroite (Rome détestait les rois); et quand on a abandonné ces limites avec Sylla puis Jules César, ça a achevé la République.
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@JacqBens Une enquête a été ouverte, et j'imagine qu'on n'en entendra plus parler. 🫤␤␤(Le problème de l'actualité, en général, c'est que ça manque cruellement de suivi, il n'y a pas moyen de s'«abonner» aux nouvelles sur un sujet donné.)
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@monsieurpuyo La tournure apparaît trois fois dedans, en tout cas. 😄
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Avec le alt-text: pic.x.com/CMYrqBr93Z
Considérations juridiques ou politiques mises à part, c'était (j'espère que c'est «c'était» et pas «c'est» 😅) un trou de sécurité informatique complètement hallucinant du système des impôts français, là.␤␤N'importe qui pouvait changer le prénom de n'importe qui d'autre‽ 🤯😱 pic.x.com/YHWJxeWAWA x.com/CJuridiques/st…
Billet de blog qui ressemble plus à un coup de gueule contre la notion de «chef»: madore.org/~david/weblog/…
Cette scène ressemble bien à une tentative de meurtre par des policiers en voiture sur un motard. Et c'est là qu'on se dit heureusement ①que plein de gens ont des dashcams qui filment tout sur la route, et ②qu'on a (encore) le droit de filmer la police. youtube.com/watch?v=jWTysW…
RT @l_envolee: Envoi du N°62 du journal contre toutes les prisons à #sarkozyenprison 1 des plus grands enfermeurs de France, abonné d'offic…
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PS: An interesting byproduct of this construction is that it shows one can find E of arbitrarily Turing degree such that E × (ℕ∖E) and (ℕ∖E) × E are computably separable (since P has the same Turing degree as r in the above).
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@AmirLivneBaron Did it perform any Web searches when writing this answer? Because the fact that it found exactly the same argument as I did makes me wonder whether it might have found the answer I had posted on Bluesky just before: bsky.app/profile/gro-ts…
RT @GenevieveMadore: pic.x.com/SEGev94Gx0
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(“Andrew Windsor” or “Andrew Mountbatten” or “Andrew Mountbatten-Windsor” or “Andrew Schleswig-Holstein-Sonderburg-Glücksburg / Saxe-Coburg-Gotha”, or whatever it should be. This family doesn't even know its own surname. 🙄)
Strange how even the people calling for King Charles's brother to be stripped of his royal titles and prerogatives still refer to him as “Prince Andrew” rather than “Andrew Windsor”. If you don't want him to be “Prince Andrew”, maybe don't call him “Prince Andrew”?
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@AmirLivneBaron … Anyway, I found a solution on my own (🔽). But I'm still curious to see what ChatGPT's might have looked like. x.com/gro_tsen/statu…
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@AmirLivneBaron Link doesn't work for me: it says “Conversation inaccessible or not found. You may need to switch accounts or request access if this conversation exists.” (maybe you need to change some kind of share option). …
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Update: ① and ② are NOT equivalent, as the following example (which satisfies ② but not ① and also not ③) shows: 🔽 x.com/gro_tsen/statu…
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… so they are not computably separable. On the other hand, given (r,s) in P×Q ∪ Q×P, it's obvious to decide which is in P and which in Q: the smaller one is in P and the larger one is in Q; and this test can be done computably, and can be extended to be defined everywhere. ∎
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… By coding rational numbers by integers in a computable way, I might as well search for P,Q⊆ℚ. Let z be a arbitrary fixed noncomputable real number. Let P = {r∈ℚ : r<z} and Q = {r∈ℚ : r>z} be the lower and upper cuts defining z. They are complements and noncomputable, …
Found it! 😊 And, of course, like the egg of Columbus, once we know the trick, it seems so ridiculously obvious one wonders how it might even have been a question. 😅␤␤So, here's how to construct P,Q⊆ℕ recursively inseparable, but with P×Q and Q×P recursively separable. … ⤵️ x.com/gro_tsen/statu…
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@laurentbercot Nothing in particular, and certainly nothing different from what I got.␤␤But I now have an interesting endless source of exam questions: ask a math question to an AI, copy-paste its answer, and ask students “is this AI-generated reasoning correct? if not, explain where”. 😁
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Interesting how Grok's response to being shown the error and being told not to hallucinate is a very terse admission that it can't solve the problem x.com/i/grok/share/Z… — whereas ChatGPT (cf. supra) offered a more lengthy analysis of the error + apology + suggestions.
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Equally bullshitesque answer from Grok, who gave me the opposite answer from ChatGPT, then proceeded to construct a counterexample which is even more wrong: x.com/i/grok/share/R… (I'm out of quota so for now I can't see how it reacts to the error being pointed out)
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I don't know how hard the question is because I don't have the answer myself (see 🔽). But that it can't solve it isn't really the point. That it tries to give a bullshit answer, rather say “I can't solve this”, OTOH, makes the tool pretty useless now. x.com/gro_tsen/statu…
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Note that this was produced after a lot of thinking (some of which seemed to go in reasonable directions, but not far). However, ChatGPT never seemed to try other problem-solving techniques like search for counterexamples, try in simpler cases or with additional assumptions, etc.
I was curious about how good the current free ChatGPT (in “thinking” mode) is on grad-level math questions; and it is still trying to bullshit me by giving a superficially plausible but actually nonsensical “proof”: chatgpt.com/share/68f7eade…
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… because I thought I was dealing with two notions rather than (perhaps!) four. So now my questions are: do ②, ③ and ④ have std names? do they admit easier equivalents or reformulations? is ② in fact equivalent to ①? also, what does ④ mean if Q=ℕ∖P? ❧ Thoughts? •19/19
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The above thread is confused and/or wrong — but somehow ended up asking a possibly interesting which was not the question that I intended to ask. Here is an attempt to clean up the mess: 🧵🔽 x.com/gro_tsen/statu…
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What I do NOT know so far is whether ①⇒② is in fact an equivalence, or whether they are genuinely different notions. This is the “accidentally interesting” question I asked even though I didn't mean to. My initial thread was confused and/or wrong … •18/19
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On the other hand they DO satisfy ④, because given a program that halts and another that doesn't we can just run them in parallel to decide which one halts and which one doesn't. ∴ This example shows that ③⇒④ isn't reversible (and ④ doesn't imply ②∨③). •17/19
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… and thus by asking our hypothetical ②-solver (cross-separator) whether (e₀,e₁) ∈ H × (ℕ∖H) or (e₀,e₁) ∈ (ℕ∖H) × H, we computably separate H₀ and H₁ (note we always terminate!): impossible! This proves that P:=H and Q:=(ℕ∖H) don't satisfy ② either. ∎ •16/19
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… Indeed, given e we can computably generate e₀ which terminates iff φ_e(0)↓=0 (add a loop if result is ≠0), and similarly also e₁ which terminates iff φ_e(0)↓=1. So given e, we have e ∈ H₀ iff (e₀,e₁) ∈ H × (ℕ∖H), and e ∈ H₁ iff (e₀,e₁) ∈ (ℕ∖H) × H … •15/19
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I claim they also don't satisfy ②: indeed, let me prove that if they did (if H and ℕ∖H were computably cross-separable, i.e., if H × (ℕ∖H) and (ℕ∖H) × H were computably separable), then we could separate H₀ and H₁ of the previous example. … •14/19
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‣ Now consider the example of P := H := {e : φ_e(0)↓} and Q := ℕ∖H its complement. This does not satisfy ① as H isn't computable, and also not ③ (since ① and ③ are clearly equivalent when P and Q are complement of one another). … •13/19
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… however, they DO satisfy ③ (and hence ④) because given e in H₀∪H₁ we can simply run it until it stops to decide whether it's in H₀ or in H₁. So this example shows that neither implication ①⇒③ nor ②⇒④ are reversible. •12/19
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‣ Now consider P := H₀ := {e : φ_e(0)↓ = 0} and Q := H₁ := {e : φ_e(0)↓ = 1}. It is a standard fact of computability that they are computably inseparable (i.e., fail ①); but they also fail ② as @JeanAbouSamra points out on Bluesky 🔽 bsky.app/profile/jeanas… ; … •11/19 pic.x.com/HxOVu7EkzX
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❦ We just defined 4 different notions of “separating” P and Q. Implications ①⇒③ and ②⇒④ are trivial. It's also easy to see that ①⇒② and ③⇒④ by just forgetting the second component of a pair. Are any of these implications reversible? Let's see some examples! •10/19
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Informally, this means that there is a way, given a pair of elements, and provided one is in P and the other in Q, to (computably!) tell which is which. If this hypothesis isn't satisfied, you can reply anything or even fail to terminate. •9/19
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‣ Definition ④ (you can see where this is going!): if P,Q⊆ℕ (necessarily disjoint), let us say that P,Q are “semicomputably cross-separable” (still NOT standard terminology) when P×Q and Q×P are semicomputably separable, as subsets of ℕ² (cf. definition ③). •8/19
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Informally, this means that there is a way, giving an element of P or Q, to computably decide whether it is in P or in Q; if it's in neither, you can reply anything, but this time you can even fail to terminate (contra ①). •7/19
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‣ Definition ③: if P,Q⊆ℕ (necessarily disjoint), let us say that P,Q are “semicomputably separable” (again, NOT standard terminology) when there exists h:ℕ⇢{0,1} partial computable, defined at least on P∪Q, such that h is identically 0 on P and identically 1 on Q. •6/19
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Informally, this means that this time we are given a pair of elements, and provided one is in P and the other in Q we are (computably!) supposed to tell which is which. Again, if this hypothesis isn't satisfied, you can reply anything, but you must still terminate. •5/19
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‣ Definition ②: again if P,Q⊆ℕ (necessarily disjoint), let us say that P,Q are “computably cross-separable” (NOT standard terminology) when P×Q and Q×P are computably separable, as subsets of ℕ² (which we can view as subsets of ℕ using a standard encoding of pairs). •4/19
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Informally, P and Q being “computably inseparable” means that there is a way, giving an element of ℕ, to computably decide whether it is in P or in Q; if it's in neither, you can reply anything, but you MUST reply in finite time. •3/19
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‣ Definition ①: if P,Q⊆ℕ (necessarily disjoint), we say that P,Q are “computably separable” (this is standard terminology) when there exists h:ℕ→{0,1} computable, defined on all of ℕ, such that h is identically 0 on P and identically 1 on Q. •2/19
OK: the question I asked 🔽 was not the question I meant to ask, but it seems to be interesting in itself, so now I have even more questions. Apologies! Let me try to dispel the confusion and state things clearly and correctly. 🧵⤵️ •1/19 x.com/gro_tsen/statu…
RT @AltcoinPsycho: gotta love seeing 95% of crypto down because of an AWS outage␤␤very decentralized - great work lads 👍
RT @internetofshit: I genuinely cannot believe a BED stops working because of an amazon outage. the jokes are literally writing themselves. x.com/m_franceschett…
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Aussi: 85% des Français sont d'accord avec l'affirmation «on a besoin d'un vrai chef en France pour remettre de l'ordre». 🤢😱💀␤␤(Et l'approbation de cette affirmation est majoritaire chez les sympathisants de TOUS les partis politiques et dans TOUTES les classes sociales. 😭)
Certaines des réponses à ce sondage sont absolument terrifiantes quant à l'état d'esprit des Français, par exemple leur pessimisme quant à l'avenir.␤␤(Pessimisme que je partage… entre autres justement à cause de l'état d'esprit des Français. 😬) x.com/mathieugallard…
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Bref, j'ai voulu éviter la pluie, j'ai perdu 15min et j'ai quand même pris la pluie. C'est ça la magie des transports en commun en Île-de-France.
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J'avais le choix entre métro 14+6 ou 14+7 (ou juste 14), j'ai bêtement choisi le premier, ne sachant pas que ①le métro 6 s'arrête en ce moment à Place d'Italie, et ②il est, en plus complètement cassé cet après-midi.
48 minutes pour rentrer en transports en commun de l'IRIF à chez moi (2.1km à vol d'oiseau, ~35min à pied). 💀 Et quand je dis «en transports en commun», j'ai pris le métro jusqu'à Nationale et j'ai abandonné et fini à pied.
RT @haveigotnews: The thieves who carried out the Louvre jewellery raid are described as ‘professional and effective, with a well-prepared…
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Basically, “P×Q and Q×P are computably inseparable” means that if you're given an element of P and one of Q you can't computably decide which is which, whereas “P and Q are computably inseparable” means that just given an element of P∪Q you can't tell whether it's in P or in Q.
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Note that “P×Q and Q×P are computably inseparable” is stronger than “P and Q are computably inseparable”: for example, if P ✺or✺ Q is computably enumerable, or co-c.e., then P×Q and Q×P are computably separable.
RT @gine_robert: C'est là qu'on regrette de ne pas avoir de distinction entre le datif et le génitif en français x.com/clem_garin/sta…
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(I mean computably inseparable as subsets of ℕ², of course.)
If P,Q⊆ℕ (are disjoint), is there a simpler equivalent reformulation of the assertion “P×Q and Q×P are computably inseparable”?
Impasse Damesme, #Paris13 pic.x.com/MhQXBhtcUI
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… it's meant to provoke indignation, resentment, humiliation and suffering from “liberals” (and, indeed, it is working exactly as intended). The MAGA crowd will enjoy these more than the message itself. •7/7␤␤PS: Relevant ‘Guardian’ opinion piece: theguardian.com/commentisfree/…
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The trolling here isn't exactly subtle. It says “you hate us? let's make you hate us even more, because there's nothing you can do about it”. It screams “væ victis!”. The message isn't meant for their own supporters (who don't actually want a king), … •6/7
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(And yes, Vance — or whoever handles his PR — knows exactly what he's doing by posting this on Bluesky and not on Twitter. He knows this will cause maximal outrage and consternation. Trump is just being crass, but Vance's video is far more distressing.) •5/7
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… while the Vice-President posted on Bluesky(!) bsky.app/profile/jd-van… another AI-generated video of Trump donning regal insignia while key Democrats kneel and bow before him. •4/7 pic.x.com/6Cv5L9ZVT4
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… the President of the United States posted on Truth Social truthsocial.com/@realDonaldTru… an AI-generated video of himself wearing a crown, flying a jet plane and dumping shit on protesters' heads, … •3/7 pic.x.com/08BNtryX3T
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… the obvious reaction to the protests would be to dismiss the protesters' accusations as an overreaction, to claim that the executive is exercising its normal powers in accordance to article II of the Constitution of the United States, yada yada. But instead … •2/7
As I've repeatedly said, I believe a significant proportion of Trump supporters adore him not so much because they like what he does or says, but because he enrages people they despise (in short, “liberals”). Reactions to “No Kings” protests illustrate this beautifully: … •1/7
RT @Laetitia_Simoes: 1/ 🛑APPEL À TÉMOIN : je n’ai jamais fait ça, mais aujourd’hui j’ai besoin de vous !␤Vendredi matin vers 9h15, je roula…
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@plain_simon … Still, omniscience principles can quickly turn into a maze of similarly-looking statements. The (interesting!) paper “The Weak Kőnig Lemma, Brouwer’s Fan Theorem, De Morgan’s Law, and Dependent Choice” by Berger, Ishihara and Schuster is a good example. ejournals.eu/en/journal/rep…
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@plain_simon … that being said, in practice, only a handful turn out to be uninteresting (the general rule of thumb is that constructive math prefers “positive” statements like “x>y” or “there exists yada-yada” and avoids negations). …
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@plain_simon There are an infinite number of ways to rewrite any classical statement in constructive math. Even the tautologically true statement has an infinite number in pure propositional calculus with just one variable: see commons.wikimedia.org/wiki/File:Rieg… (all but the bottom 4 nodes) …
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@ncfavier Maybe it's worth opening a math.meta.stackexchange.com question “how can we make constructive math questions better received on MSE?” I'm not too active on MSE, but if you want a crack at it, I encourage you to do so.
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@ncfavier It is indeed infuriating. That being said, people who ask constructive math questions would do well to start with a standardized header saying something like “this question is about constructive mathematics [link to Wikipedia] and is obviously trivial in classical mathematics”.
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@pointed_max It is indeed infuriating. But there are currently several votes for reopening, so it will probably happen (not that it matters much anyway).
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Link to MSE answer is here: math.stackexchange.com/a/5102698/84253
I answered a Math StackExchange question about constructive math, and used the occasion to recall a few standard principles in this domain. pic.x.com/BlOMfYE5PC
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@RogierBrussee … then we can choose one N(k) for each k). There are actually many situations where this occurs (e.g., if we have either classical logic or countable choice we can identify Cauchy and Dedekind real numbers, for analogous reasons).
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@RogierBrussee … the assertion “every inhabited set of natural numbers has a smallest element” is not constructively valid. So your proof is valid if you have EITHER classical logic (in which case your N(ε) is explicit) OR countable choice (provided we replace ε by 2^−k; …
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@RogierBrussee Choice is basically the act of changing a ∀∃ quantifier combination to ∃∀ where the the ∃ is a function. Here you are changing “∀ε>0. ∃n” to “∃N(ε). ∀ε>0”. Now in your proof 🔽 you make N(ε) explicit. But … x.com/RogierBrussee/…
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@GavinZJL @iansamir18 (The diameter reformulation of (☆) would be to say that liminf diam(E_N) = 0. Of course one can point out that diam(E_N) is monotonically decreasing so liminf diam(E_N) = 0 is equivalent to lim diam(E_N) = 0, but this isn't easier than noting (☆)⇒(★) anyway.)
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@GavinZJL @iansamir18 I just checked and I didn't see (☆) in it. There is an equivalent definition in terms of diameters, but it's more a reformulation of (★) than of (☆). pic.x.com/hkcTenbk1v
Some people wrote a linguistics paper on how the gender of “Covid” in French settled over time, in three continents: doi.org/10.1017/cnj.20… 🤩
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@iansamir18 Precisely. So a good textbook should probably point out both versions. And it surprises me that so few do!
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@RogierBrussee Some diehard constructivist mathematicians might object that your version requires use of countable choice, however.
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… I agree with JDH that saying that Turing “essentially” proved the result is probably the best compromise here: it's a bit vague, but avoids sacrificing historical accuracy while still giving credit where it is due.
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… It is indeed a delicate balance to avoid saying something that is historically incorrect but still give Turing the credit he clearly deserves even though he didn't state the exact result we now consider the cornerstone of all the theory! …
As J. D. Hamkins carefully explains 🔽, Turing never actually proved the undecidability of the halting problem that everyone attributes to him; nevertheless, he laid the foundations and all the essential ideas for such a proof. So how should we properly credit him? … x.com/JDHamkins/stat…
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@Ognifedefingo Because there's one less variable and one less quantifier.
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@Dr_S_Sydoryk C'était dans un café (par ailleurs très calme), mais il faut vraiment que je pense à apporter des bouchons d'oreilles ou un casque à compensation de bruit.
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JPP ça fait une demi-heure que ça dure, je sais tout sur sa vie et de sa santé, de ses intestins à ses implants dentaires en passant par son épisode dépressif qui lui a fait prendre du poids. 💀
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MAIS JE NE VEUX PAS SAVOIR POUR VOTRE COLOSCOPIE MADAME! 😩
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Et elle se plaint des gosses malpolis, en plus. Je suis sûr que les gosses en question savent utiliser un clavier de portable, s'envoyer des messages et ne pas faire profiter tout le monde de leurs conversations.
Les boomers qui tiennent des conversations interminables au téléphone à voix très forte dans les lieux publics où on apprécierait un peu de calme. 🤬
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@PLT_cheater @ArthurB (Also, the sequence of partial sums of 1/n is definitely NOT a Cauchy sequence, since it's not even bounded.)
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@PLT_cheater @ArthurB I don't know what you mean by «correct» and «incorrect» senses, but the conditions (★) and (☆) of the tweet at the top of this thread are equivalent, as I proved in the very next tweet: x.com/gro_tsen/statu…
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@ArthurB Oh really? That's interesting. Whence did you learn it?
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Asked on MSE: math.stackexchange.com/q/5102407/84253
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I can imagine various reasons why (★) would be slightly more convenient to work with, but I'm still surprised I've never seen (AFAICT) any text use (☆) as definition or even explicitly point out the equivalence. Has anyone seen it before?
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Proof of equivalence: (★)⇒(☆) is trivial. For (☆)⇒(★), given ε, apply (☆) to ε/2, giving n such that if r≥n then |u_r−u_n| < ε/2; now if p,q≥n, then |u_p−u_q| ≤ |u_p−u_n| + |u_n−u_q| < ε/2 + ε/2 = ε. ∎␤␤(This proof is valid constructively and doesn't use Choice.)
The definition of a Cauchy sequence (u_n) is:␤␤(★) ∀ε>0. ∃n. ∀p,q≥n. |u_p − u_q| < ε␤␤But it can also be given as:␤␤(☆) ∀ε>0. ∃n. ∀r≥n. |u_r − u_n| < ε␤␤This seems a bit simpler, if less symmetric. Is there some reason nobody ever seems to write it that way?
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@Hasen_Judi Exactly. As the GNU General Public License states:␤«␤The “source code” for a work means the preferred form of the work for making modifications to it. “Object code” means any non-source form of a work.␤»␤⇒ The source is the part you keep and actually work on to make changes.
RT @CanuckCreator: Sitting in the parking lot at the mall waiting for my car to finish a software update so I can turn it off. I love the f…
RT @Ligne10_RATP: [Inauguration] Bienvenue à bord : le #MF19 a effectué son premier voyage sur la #ligne10 ! 🥳␤Ce métro nouvelle génératio…
RT @Hasen_Judi: I keep seeing people pretend that English now is the programming language and the LLM generated code is better understood a… x.com/dvassallo/stat…
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@JacqBens … D'ailleurs, on ne met pas la couleur ou longueur des cheveux pour cette raison: les gens ont tout à fait le droit de se les teindre ou couper comme ils veulent, donc ça n'aide pas à les reconnaître.
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@JacqBens … écrit sur leur carte d'identité et qui apparaissent de tout point de vue comme des femmes (sauf à mener un examen médical approfondi que la police n'a pas le droit de faire), ou vice versa. Donc l'intérêt comme description me semble très faible. …
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@JacqBens Je ne serais pas forcément contre avoir l'information «ressemble à un homme» ou «…à une femme» purement descriptive et non normative sur une pièce d'identité (même si ça me semble redondant avec la photo), mais justement, en l'occurrence, il y a des personnes qui ont «homme» …
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@antoineducros («Faire effet sur un tiers» → je pense par exemple à des lois qui sanctionneraient les employeurs discriminant selon le sexe, avec un contrôle selon des déclarations volontaires des employés, cachées à l'employeur pour éviter les pressions.)
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@antoineducros Par ailleurs, même cette mesure plus radicale n'entraînerait pas forcément de disparition de toutes les lois paritaires: la déclaration peut être volontaire, et ça peut marcher si elle est contrôlée par l'opinion publique (en politique) ou si elle fait effet sur un tiers.
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@antoineducros Non, c'est juste une suppression de la mention du sexe sur la carte d'identité, pas sa disparition totale de l'état-civil (ce avec quoi je serais aussi d'accord, mais qui va beaucoup plus loin).
On me signale cette proposition de loi visant à supprimer la mention du sexe sur les cartes nationales d'identité françaises: assemblee-nationale.fr/dyn/17/textes/…␤␤Je suis complètement d'accord avec ça, et l'exposé des motifs est intéressant.
RT @FFmpeg: Arguably the most brilliant engineer in FFmpeg left because of this. He reverse engineered dozens of codecs by hand as a volunt… x.com/FFmpeg/status/…
RT @FFmpeg: Our friends at dav1d showing us the value of specific domain knowledge.␤␤dav1d was written by people in their basements, libgav…
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@JacqBens Mittag-Leffler is an obvious candidate because he and Nobel knew each other (and had their ups and downs), and he [ML] himself ended up creating a prize of sorts for mathematics, and also influencing various Nobel prizes (in particular getting Marie Curie named).
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(Everyone, of course, except the editors of Wikipedia who will face an endless stupid semantic debate on whether the MAGA Nobel Prize is or is not a Nobel Prize.)
All the US conservatives really need to do is create a “Heritage Foundation Prize for Making America Great Again in Memory of Alfred Nobel” with an extra large gold medal and award it to Donald Trump, and everyone will be happy! x.com/gro_tsen/statu…
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Or, as I pointed out earlier: x.com/gro_tsen/statu…
Interesting that the Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel managed to weasel itself so successfully into the “Nobel Prize” list that even the official account seems to forgets that there is no more Nobel Prize in Economics than in Mathematics. x.com/NobelPrize/sta…
I seem to have mislaid my Bow of burning gold, my Arrows of desire, my Spear and my Chariot of fire. If you find them, please bring them to me ASAP.
J'ai trouvé étonnamment intéressante la série documentaire diffusée sur Arte “Monaco: La grande histoire d'un micro-état” (de Frédéric Compain, 3×45min). Alors que je pensais le sujet pas super passionnant a priori. arte.tv/fr/videos/RC-0…
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… J'espère de même que les ministres du nouveau gouvernement 🇫🇷 ont été choisis pour leur capacité à expédier les affaires courantes.
Quelqu'un que j'avais croisé dans une association LGBT (il y a ~25 ans) m'avait blagué qu'il choisissait ses compagnons pour leurs qualités comme ex parce qu'ils passeraient certainement beaucoup plus de temps dans l'état «ex» que dans l'état «copain».␤␤…
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… and having a smartphone app to “perform the function of a smartphone” is a bit nondescriptive as to what that app actually does.
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Also this 🔽: a 📱 smartphone has so many functions whereas a 📞 telephone receiver has only one. The 📱 icon could refer to any or all of the functions of a smartphone, … x.com/JeanDellass/st…
Let's also change the letter ‘A’ to a real bull's head because people are too stupid to deal with ideas. x.com/LeakerApple/st…
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This is from MathOverflow: mathoverflow.net/users?tab=Repu…
Oh, look, I'm just above Terence Tao (this year) in Meaningless Internet Points! 🥳 pic.x.com/G2SNQK9P2S
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@Blaxapate @antoineducros Oui, tout à fait. Ce qui suggère que ces définitions ne sont pas franchement terribles.
Yesterday, someone said to me:␤␤“The definition of ‘leisure’ is what you do with your time and wouldn't want someone else to do in your stead.”␤␤I really like this formulation.
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… causing it to enter a special mode which subtly breaks the numeric keypad. (And before running a program like “cat”, zsh sends “␛[?1l” which restores the keypad to a saner mode.)␤␤WHY this shit even exists or WHY zsh decides to send it is lost to the mists of time. 🤷
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(This is not because of a misconfiguration on my part: I checked with a pristine config.)␤␤The reason is some incomprehensibly bizarre shit like only Unix can invent: zsh sends the arcane “␛[?1h” (where ‘␛’ stands for escape, i.e., \033) control sequence to the terminal … pic.x.com/2qA1mssLLt
Under Linux, if I open zsh in an xterm (or gnome-terminal) and press the ‘+’ key of the numeric keypad, instead of entering ‘+’ it rings the bell. 🤦␤␤Oddly enough, if I type “cat” and type ‘+’ inside cat, it works fine. The keypad ‘+’ is only broken inside zsh itself.␤␤Why? …
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Pour moi c'est ça le truc qui rend les tramways souvent merdiques comme moyens de transport (et encore, celui-là avec le T11 est sans doute le moins pourri en ÎdF): beaucoup trop d'arrêts, donc beaucoup trop rapprochés, par rapport à la très faible capacité d'accélération.
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… Donc apparemment il accélère ou freine à 0.5m/s² (soit 5% de g). Ou un 0–100km/h en… 1 min. 😬␤␤Ce qui veut aussi dire que:␤␤‣ Chaque arrêt fait perdre 2min en plus du temps de l'arrêt lui-même.␤␤‣ S'ils sont séparés de <1600m on n'atteint même pas la vitesse de croisière.
Courbe de vitesse en fonction de la distance relevé tout à l'heure par mon GPS pour un trajet du tram T13 d'Île-de-France entre Camp des Loges et Saint-Cyr.␤␤Manifestement il lui faut environ 800m pour accélérer ou freiner à vitesse de pointe (100km/h). … pic.x.com/9k9NUHkvt9
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@ArthurB Cc @Conscrit_Neuneu
Love how the Wikipedia article on woodlice has sections on them as pests, food(‽) and pets. Such creatures of many talents! en.wikipedia.org/wiki/Woodlouse pic.x.com/2aeoCb1xv9
RT @VarlanOlivier: Sébastien Lecornu tentant d’échapper au poste de premier ministre : pic.x.com/bdsYgEZZwH
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@antoineducros OK, ça a l'air de marcher, mais heureusement qu'on n'a pas un bout de caillou pile sur le méridien 180°.
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@monsieurpuyo Probably, but I don't know who thinks of the international date line as separating the easternmost and westernmost parts of the globe, except insofar as… well, dates and times… are concerned.
What does that even mean? 🙄 x.com/amazingmap/sta…
RT @Toyec_PE: Aujourd'hui, Lecornu est Premier Ministre. Ou peut-être hier, je ne sais pas. J'ai reçu un télégramme de l'AFP : "Le Présiden…
RT @GenevieveMadore: pic.x.com/uc1JB8eqY6
RT @piotelat: @pbeyssac Histoire d'envoyer un message aux députés, même si ça se décide au niveau Européen (et que la démocratie en France,…
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The Guardian: “Norway braces for Trump’s reaction if he does not win Nobel peace prize — US president may impose tariffs, demand higher Nato contributions or even declare Norway an enemy, analyst says” theguardian.com/world/2025/oct…
RT @depressionlesss: pic.x.com/I0cdhj222u
RT @niubi: I did a translation of all 6 related announcements here. Today's actions go way beyond semiconductors. You company needs drill b… x.com/aphysicist/sta…
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@laurentbercot Ah, maybe what I thought were his eyeballs are actually his eyelids. Or maybe what you thought were his eyelids are actually his eyeballs. Or maybe it's a what-color-is-this-dress kind of thing.
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@laurentbercot I'm sorry, but my old guy does the no-fun unamused disapproval stare better than your young guy does. It's an old recipe kept by Orthodox monks for centuries.
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Original image: commons.wikimedia.org/wiki/File:Sain…
A new meme just dropped. pic.x.com/1qtxGiq9p7
Incidentally: how did it turn out to be that the Nobel peace prize is handed out by Norway while every other Nobel prize is handed out by Sweden? (Yes, I know Norway and Sweden were in some kind of union when Nobel was alive. My question is who decided how to split tasks.) x.com/gro_tsen/statu…
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Well, the BBC has a news article about the Norwegian Nobel committee: bbc.com/news/articles/… (and apparently you can show their faces).
@laurentbercot I thought you might like this post from the other network. bsky.app/profile/did:pl… pic.x.com/Z4xHHrobCe
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J'oubliais de lier vers mon billet de blog de l'an dernier (avant que je découvre l'existence des V Pen): madore.org/~david/weblog/…
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@bzavr Je pose la feuille devant ma fenêtre (et je tâcherai de penser à la tourner et repositionner de temps à autres).
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Je précise que je n'ai pas d'actions chez Pilot. J'aime juste bien les trucs qui se déclinent en plein de variations de façon assez systématique.␤␤Et là, ça m'énerve que le nombre de couleurs ne soit pas le même (7, 4, 8 ou 6? wtf, Pilot‽) d'une gamme à l'autre. 😠 pic.x.com/J2vXZIKArR
Début d'une expérience Hautement Scientifique pour comparer les encres de tous les stylos de la game Pilot, leur effet sur mon écriture, et comment ils vieillissent avec le temps et la lumière. pic.x.com/6l0HWEvWub
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@GenevieveMadore @OABA_Off Même sans être doué pour ce jeu, je vois tout de suite: l'oiseau à gauche qui bat d'une aile et pas de l'autre, les mains qui surgissent de nulle part, le colisée qui apparaît deux fois, et la carte derrière très créative dans sa géographie de la mer Caspienne.
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@GenevieveMadore @OABA_Off Ils n'auraient pas pu trouver des vraies photos d'animaux pour illustrer (si possible européens… et pas que des vertébrés…), au lieu de faire dessiner leur afficher par une IA au rabais?
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For example, if a dictator speaks of “12.34% of the dissidents we arrested”, you can conclude that they arrested ≥154 people (or that they aren't rounding correctly, or that they're lying… I've actually caught some very suspicious stats that way!).
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This has an interesting application: if someone speaks of “12.34% of our foobars” (and if they rounded correctly!), then by the computation of the previous tweet, you can deduce that they have at least 154 foobars. Because no fraction with fewer would round to 0.1234.
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Random example: what is the simplest rational between 0.12335 and 0.12345? Since 0.12335 = [0; 8, 9, 2, 1, 9, 9] and 0.12345 = [0; 8, 9, 1, 21, 1, 1, 5], it is [0; 8, 9, 2] = 19/154 (indeed, this is 0.12337662…).
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If you know what the Stern-Brocot tree is, the answer is pretty obvious. Otherwise, the problem will be very mysterious. x.com/gro_tsen/statu…
Stumbled again upon this question: given p≤q real numbers, how to algorithmically find the rational number n/k with smallest possible denominator k and lying between them, p ≤ n/k ≤ q (that is: [k⋅p,k⋅q] ∩ ℤ ≠ ∅)? x.com/gro_tsen/statu…
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Here I had to replace “<ref name="Duoandikoetxea-2001" />” by “<ref>{{harvnb|Duoandikoetxea|2001|loc=Thm. 8.3}}</ref>” to cite theorem 8.3 specifically. How do you guess this kind of shit?␤␤Next time I'll just add “theorem 8.3” in the text and let someone else clean it up! 🤬
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… that every time I need to add a reference to a Wikipedia article, I spend dozens of minutes trying to read the shit that's supposed to be the “documentation”, then randomly try out stuff, and eventually give up and ask ChatGPT for help. chatgpt.com/share/68e6308a… 😭
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… or how they interact) en.wikipedia.org/wiki/Wikipedia… — and also the section preview doesn't work on citations because the previewer is too stupid to load references from the entire article (🤦), …
Wikipedia (rightly!) wants articles to cite their sources, but the maze of citation tags and templates is so incomprehensible (there's <ref>…</ref> and {{cite}} and {{citation}} and {{r}} and {{harv}} and {{reflist}} and <references /> and I don't know what else …
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#ChatControl projects, under pretense of fighting child sex abuse, to put ALL private digital communications of 🇪🇺 citizens under automated surveillance.␤␤Here's where to learn more about it and how to act against it: fightchatcontrol.eu
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⚠️ But a blocking minority is not a majority against. The issue WILL come back again, and again, as long as there isn't a clear block against this mass surveillance project. Citizens from all EU states should try to raise awareness about the dangers it poses to our private lives.
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It was thought that 🇩🇪 would change its position to “pro-surveillance”, but last-minute activism from German citizens seems to have paid off. 👍 With Germany still opposed, opposition to #ChatControl still appears to have a blocking minority in Council. x.com/signalapp/stat…
Great news! The disastrous dystopian massive surveillance #ChatControl project (of automated surveillance of private electronic communications) seems to have once again failed to gather a sufficient majority in the 🇪🇺 Council. 🥳 x.com/echo_pbreyer/s…
RT @echo_pbreyer: 🇪🇺YOU ARE AMAZING: ❤️ Your protest stopped #ChatControl! I hear Germany isn't caving in; so there's no majority in the EU…
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@Jilcaesel Pour dire les choses autrement: je cite l'article que j'ai moi-même utilisé pour m'informer. Or je vais généralement sur WP-en en premier (ici, je lis l'allemand trop lentement pour faire l'effort de lire WP-de, même si ça m'arrive dans d'autres cas).
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C'est une version développée de ce fil: x.com/gro_tsen/statu…
Bon ben du coup j'ai ranté dans mon blog sur les régimes parlementaires et sur l'idée que ça conduit forcément à l'instabilité gouvernementale et/ou à de longues négociations de coalition: madore.org/~david/weblog/…
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@Jilcaesel Parce que dans >95% des cas l'article Wikipédia en anglais me semble bien meilleur que celui en français. Parfois je vérifie, et si je vois une exception, je cite l'article en français (notamment s'il s'agit d'un concept franco-français).
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(Leur nom de famille se prononce de la même manière.)
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… et Carlo Schmid en.wikipedia.org/wiki/Carlo_Sch… (qui était social-démocrate, a qui a participé à l'écriture de la Loi fondamentale actuelle).
#ClubContexte Parmi les grands constitutionnalistes allemands, il ne faut pas confondre Carl Schmitt en.wikipedia.org/wiki/Carl_Schm… (qui était nazi, et qui a participé à détruire la république de Weimar) …
«En essayant continuellement, on finit par réussir… Donc plus ça rate, plus on a de chances que ça marche.» (devise Shadok) x.com/canardenchaine…
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… or un décret publié au dernier JORF fait exactement ça (félicitations à Bruno Le Maire, donc, pour sa démission du poste de ministre démissionnaire): legifrance.gouv.fr/jorf/id/JORFTE… pic.x.com/9gUQzMTfRu
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«On peut néanmoins admettre que le Président de la République puisse valablement, par décret, démettre individuellement un ministre, et confier le soin d’expédier les affaires courantes relevant de ses attributions à un autre des ministres du Gouvernement sortant.»
En juillet 2024, dans une note (non publiée 🤬) du Secrétariat Général du Gouvernement sur l'expédition des affaires courantes, le SGG ne savait pas bien si un ministre démissionnaire pouvait démissionner: pic.x.com/gANdoEFm44 x.com/gro_tsen/statu…
RT @laputassiere: 🔴NOTE DE SERVICE␤Le pot de bienvenue de Bruno Le Maire, initialement prévu ce jour à 13h, est annulé et remplacé par un p…
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And I hope they don't have any plans to visit the US any time soon, or have any assets or family there, because the revenge is sure to be terrible, as men of peace tend to do.
I hope the Norwegian police have prepared plans for putting the members of the Norwegian Nobel Committee under special protection this Friday when they will announce that Trump is not the laureate.
RT @CDGHospit: Pour Noël, faites un cadeau inoubliable à vos proches 🎁 pic.x.com/4DEu80LciT
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@doirme Si je ne m'abuse, c'est dans les attributions du président italien, par exemple. Ça me semble assez cohérent avec un président qui se tient en retrait de la politique politicienne mais qui peut intervenir pour déverrouiller un conflit entre le Premier ministre et le parlement.
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@doirme Et aussi, on peut très bien avoir un chef d'État élu au suffrage universel direct qui n'ait aucun choix pour nommer le Premier ministre. Il peut avoir d'autres pouvoirs (représenter l'État, nommer les plus hauts juges, dissoudre le parlement, être le chef des armées).
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@doirme À ceci près que les députés Allemands n'ont pas de date limite pour élire le chancelier, je crois, alors que je propose de le faire presque immédiatement (ce qui met la pression pour la formation de coalitions).
RT @gro_tsen: Wait, there's a prize named after a guy called “Alfred Noble” who is NOT THE SAME as the Alfred Nobel after whom the Nobel pr…
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@IanSolliec If the subject still interests you, here's a super detailed video by a guy who seems to know what he's talking about about the causes and timeline of the Iberian blackout. youtube.com/watch?v=DK8mw0… (Warning: I found it hard to follow because of the wealth of technical terms.)
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At any rate, I think a moratorium needs to be put in place: no mathematician is allowed to define a new meaning of the word “normal” until further notice. Buy yourself a thesaurus! subwiki.org/wiki/Normal_(m…
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… I wonder if there have been linguistic studies on how mathematicians choose their technical terms, and what makes them prefer certain words over others. This could be interesting.
The most overloaded terms in mathematics are probably “normal” and ”proper”, each having MANY meanings.␤␤But it's strange that certain (approximate) synonyms, like “decent” or “felicitous” aren't used at all as technical terms AFAIK (maybe because they sound too subjective?).␤␤…
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Actual link to my Bluesky account: bsky.app/profile/gro-ts…␤␤And actual link to the Mastodon bridge account: fed.brid.gy/bsky/gro-tsen.…
I don't know who needs to hear this, but my Bluesky account is now bridged to Mastodon under the name (at)gro-tsen.bsky.social@bsky.brid.gy (so you can follow my Bluesky activity by following this user on Mastodon — and I don't know what happens if you reply on Mastodon).
J'apprends que Gérard Laumon est décédé. smf.emath.fr/actualites-smf…␤␤Il a brièvement été mon directeur de thèse en 1999 (avant de me foutre à la porte parce que je ne faisais rien, et je lui en dois reconnaissance).␤␤Il était un grand mathématicien, et quelqu'un de vraiment bien.
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Et je rappelle aussi que le principe «le gouvernement reste en place jusqu'à ce qu'un autre obtienne une majorité» que je propose peut aussi fonctionner avec «le budget» à la place de «le gouvernement» (et qu'on peut supprimer les deadlines artificielles). x.com/gro_tsen/statu…
Je rappelle une fois de plus à toutes fins utiles qu'il est parfaitement possible, et même pas spécialement compliqué, d'avoir un régime politique complètement parlementaire qui évite à la fois l'instabilité gouvernementale et des longs délais pour trouver une coalition. 🧵🔽 x.com/gro_tsen/statu…
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‣ Mise à jour un an après: les pigeons de Grigny ont été retirés en février 2025. Cf. grigny91.fr/blog/lenvol-de… et bovis-fineart.com/en/fine-art-ne… pour des détails. Ils sont censés revenir quand le quartier de la Grande Borne aura été refait.
Les trois arrêts de métro à Villejuif: Léo Lagrange, Paul Vaillant-Couturier, Louis Aragon. Ça donne une idée de la couleur politique de la mairie. 😁
RT @echo_pbreyer: 🇪🇺A strong signal from Slovenia! The government rejects #ChatControl following protests from the Pirate Party and others.…
Should I try to start the trend of calling mathematical statements that are neither provable nor refutable as “adiaphorous” instead of “undecidable”? 🤔␤␤As in: “Gödel showed that first-order Peano arithmetic and related systems admit adiaphorous statements.” 🤓 x.com/gro_tsen/statu…
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There might be a subtle difference of meaning between “adiaphorous” and “adiaphoric”, but it escapes me. Maybe the first is used more figuratively. Maybe they aren't used in the same context.
#WordOfTheDay: “adiaphorous” (or “adiaphoric” or “adiaphoristic”): refers to something that is theologically or ethically indifferent; neither commanded nor forbidden; neither praiseworthy nor wrong; or by extension: neither beneficial nor harmful.
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… assuming the Council now adopts the Commission's proposal, what would be the next steps, and what options at the Parliament level would exist to either reject the text entirely or to amend it? Does the discussion entirely happen in trilogue? pic.x.com/loSmWwc9UW
A question to people who know the precise workings of the 🇪🇺 legislative procedure: according to the law tracker timeline law-tracker.europa.eu/procedure/2022… (we are at first reading) the EP plenary has “endorsed the committee decision to start interinstitutional negotiations”: … x.com/gro_tsen/statu…
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Also understand this is about a vote in the 🇪🇺 Council, not the 🇪🇺 Parliament¹. So the people to contact now are not MEPs but national MPs (in 🇩🇪: Bundestag members).␤␤1. Yes, there will also be such a vote, but sadly much has already taken place there.␤␤x.com/gro_tsen/statu…
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… meaning that the vote could never go through. But if Germany (the largest 🇪🇺 member state) changes its position from “undecided” to “for surveillance”, they have a clear majority and they win. x.com/signalapp/stat…
I know many are tired of the #ChatControl merry-go-round which seems to come up every few weeks, but understand: the issue keeps coming back bc those behind this crazy massive surveillance project didn't have a majority in the 🇪🇺 council YET. There was a blocking minority … x.com/theo/status/19…
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@stefanslab @signalapp There will also be a battle in the 🇪🇺 Parliament, and it will also be important, but the impending vote is in the 🇪🇺 Council, so MEPs have nothing to do with this. It is up to to national MPs to ask national governments how they intend to vote and position themselves.
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@stefanslab @signalapp No, Germans should not just contact their MEPs, they should contact their MPs (Bundestag members).␤␤The 🇩🇪 position mentioned above is in the 🇪🇺 Council, not the 🇪🇺 Parliament. Ministers vote in the Council, not MEPs, so Germans MPs need to raise questions to the government.
RT @lukomski_sebito: The EU is about to end private messaging!␤␤EU’s Chat Control law would scan every WhatsApp, Signal, iMessage, and emai…
RT @MichaelMjfm: pic.x.com/B1AIn4c9ZS x.com/6drinkamy_/sta…
RT @signalapp: We are alarmed by reports that Germany is on the verge of a catastrophic about-face, reversing its longstanding and principl…
Five common mistakes when drawing the moon (I think the message here isn't so much astronomy but our lack of sense of observation: these mistakes often won't jump to the eyes of non astronomy geeks even though we should all notice how the moon behaves): youtube.com/watch?v=yY7ZUI…
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@laurentbercot @ngspiensfr Aussi, je ne suis pas persuadé qu'on ait encore le droit de faire tourner un programme sur Mac OS s'il n'a pas été obtenu par l'App Store, et signé par Apple. Qui bizarrement n'aime pas les programmes permettant de tout faire.
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Les entiers naturels ne sont pas une ressource rare. Les noms mémorables, eux, en sont une.␤␤(Ainsi que les syllabes chinoises. 🔽) x.com/gro_tsen/statu… x.com/gro_tsen/statu…
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Pour résumer, je me plains notamment que c'est ridicule d'inventer des noms cons et impossibles à retenir comme «tennesse» et «oganesson» (🙄) pour des éléments qui n'ont aucune chimie (Z=117 et 118), surtout qu'ils avaient des noms décents: «ununseptium» et «ununoctium».
Je pensais qu'un sujet sur lequel je ne sais rien et je n'ai rien à dire, en l'occurrence les noms des éléments chimiques, ça donnerait un billet de blog court, mais ça n'a que médiocrement marché (même si c'est un peu moins interminable que d'habitude): madore.org/~david/weblog/…
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Presently trying to decide whether this hill is worth dying on. Probably not.
The neutron is a radioactive isotope of nilium, “nilium” being the chemical element with atomic number 0 (zero protons and zero electrons).␤␤I think nilium should be on the periodic table (in the inert gaz column, which should therefore be on the far LEFT, not right).
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(J'ai souvent besoin de ce mot.)
Un mot allemand pour désigner l'agacement qu'on ressent quand, après être allé aux toilettes (publiques) et s'être lavé les mains, on se rend compte qu'il n'y a ni serviettes ni séchoir et que si on utilise du PQ pour se sécher les mains, il se délite en petits morceaux collants?
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Ou alors on dit que non ça ne compte pas parce qu'il a été supprimé et que la Chambre des Pairs c'était autre chose. Mais alors je rétorque qu'il n'y avait pas de Sénat entre 1946 et 1958 non plus. 🤔
Le Sénat français prétend célébrer les 150 ans du «Sénat de la République» senat.fr/connaitre-le-s… — mais le Consulat était officiellement une république, non? Du coup, son «Sénat conservateur» devrait compter comme «Sénat de la République», et ça fait 225 ans en fait.
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I understand that the current kind is one type ①. Also, for some reason, US fiscal years start on Oct 1, which explains why the issue arises now (but sometimes it drags on later in the year because Congress only kicks the can down the road by means of a “continuing resolution”).
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(Type ② is completely absurd: Congress orders the federal government to collect certain taxes and spend certain amounts, but apparently it still ALSO needs to allow it to borrow certain amounts, even though they are a mathematical consequence of the first two.)
This is never clearly explained, but IIUC there are two types of government shutdowns in the US: ①those due to the appropriation bills expiring (Congress needs to pass another) and ②the even sillier ones due to the debt ceiling being reached (Congress needs to raise it).
RT @OurWorldInData: France opened a flurry of nuclear power plants in the 1980s and 1990s, giving it low-carbon electricity ever since—␤␤At…
RT @EUCourtPress: 10 years ago today, #ECJ ruled that national #dataprotection laws can apply to foreign companies that carry out real, eff…
If someone can display ads on your fridge without your consent, you do not own that fridge. x.com/internetofshit…
RT @internetofshit: honestly this is so evil␤- sell you a smart fridge␤- omg cute it can show photos and leave lil notes uwu␤~ waits a year… x.com/Dexerto/status…
RT @tenobrus: i'm about to make ten million dollars pic.x.com/3TLh4NXqoQ x.com/openai/status/…
J'ai écrit un rant dans mon blog sur la liberté d'expression: madore.org/~david/weblog/…
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@ShriekingNoises You know this network too well! 😁
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@SakumiBLR @Conscrit_Neuneu Et j'ai même retrouvé dans mon journal-où-je-note-tout que le jour où nous avons mangé ensemble au pot était le 13 avril 2005 (c'était la semaine suivant ma soutenance de thèse).
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Voici l'extrait 🔽 (le texte complet est sur fr.wikisource.org/wiki/Le_Dernie… — l'ensemble est un extraordinaire réquisitoire contre la peine de mort, qui n'a pas pris une ride). pic.x.com/4I2Hytb59H
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… pour la peine de mort quand quatre ministres («quatre hommes comme vous et moi, quatre hommes du monde») risquaient de passer à l'échafaud: x.com/gro_tsen/statu…
Les réactions de certains politiques à la condamnation de N. Sarkozy me font repenser à la manière cinglante dont Victor Hugo dénonce dans la préface de 1832 à son “Dernier Jour d'un condamné”, l'hypocrisie avec laquelle les députés se sont, en 1830, découvert une horreur …
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@EvarixGaulois @drmtgr (This is on YouTube's Web interface, on desktop. Maybe it's different on the mobile app and/or on the mobile Web interface. I've never used the former and rarely use the latter.)
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@EvarixGaulois @drmtgr You can deactivate dubbing in YouTube on a per-video basis by going in the settings (⚙️ icon) and changing the audio track to the native one (I don't have an auto-dubbed video at hand to check, but it's not hard once you know it exists). But it's not a sticky setting.
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Look, I understand more than one language. I don't think this is extraordinarily rare (outside of 🇺🇸! 😆). YouTube can deal with this.␤␤❋Offering❋ to translate (or even offering to always do it) is perfectly fine. Shoving translated content into my face is obnoxious as hell. 😡
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… they're not even consistent: just today YouTube shows me an English video with the English title translated into French (↙️) AND a French video with the French title translated into English (↘️).␤␤How does this make any bit of sense? How could a single person want to see both? pic.x.com/x1nmxi6r9N
Some time ago, YouTube started this extraordinarily annoying trick of randomly translating some (but not all!) video titles, and now even sometimes dubbing video audio (😱) without asking my opinion.␤␤But the weirdest thing about it is, …
Le graphique de l'évolution de la population de Grigny (Essonne) est assez frappant. On voit qu'il s'est… passé un truc entre 1968 (2938 habitants) et 1975 (25 653 habitants)!␤␤(Le truc, c'est la construction des grands ensembles.) pic.x.com/XXroPZBL8f
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Je me sens un peu comme le jour où j'ai remarqué que «compact disc» en anglais s'écrit avec un ‘c’ à la fin, alors que «hard disk» s'écrit avec un ‘k’.
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Par contre, le grand magasin qui tire son nom du fait qu'il est situé à l'extrémité ouest de cette rue La Fayette s'appelle bien «galeries Lafayette» et pas «galeries La Fayette». 🤔␤␤#ClubContexte
J'étais âgé de aujourd'hui années quand j'ai appris que la grande rue à Paris qui relie en gros l'Opéra au bassin de la Villette et se prolonge en avenue Jean Jaurès s'appelle «rue La Fayette» et pas «rue Lafayette» comme je le croyais. 😮
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We may have to change 毛主席语录 to The Art of the Deal in post-production, but at least we can keep the color red as it is. 👍
Typical scenes inside US academia for professors daring to teach their students that vaccines cure diseases, that climate change is real, or that transgender people exist: youtube.com/watch?v=aS8c6h…
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(J'ai écrit à ma conseillère bancaire, mais je n'ai aucune idée de quelle est la procédure pour faire corriger des erreurs techniques de CB.)
J'ai deux transactions CB effectuées en date du lundi 22 septembre dernier qui sont apparues en double sur mon compte (le lendemain, 23 septembre).␤␤Je suis chez LCL.␤␤Heureusement il s'agit de petits montants, mais si vous avez une CB chez LCL, vérifiez à tout hasard.
Je viens de recevoir un mail avec un questionnaire m'invitant à donner mon avis sur les questionnaires invitant les élèves à donner leur avis sur mes cours.␤␤J'espère qu'un questionnaire suivra pour demander l'avis de quelqu'un sur ce questionnaire!
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The problem relates to the following problem, which is how I got interested in it in the first place: what is the expected value, and what are the higher moments, of the maximum of N independent standard Gaussian variables?
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You'd think that in 2025 mathematical research would have completely solved the problem of COMPUTING THE VOLUME OF A SIMPLEX… and you'd be wrong!␤␤These links were compiled for a Twitter thread in 2021: x.com/gro_tsen/statu…
I posted an answer on MathOverflow with various bibliographical links describing what is know about the computation of the volume of a higher-dimensional simplex in spherical and hyperbolic geometry: mathoverflow.net/a/500870/17064
I asked a question on MathOverflow about a variation on Medvedev reducibility (definitions are given in the question) which seems interesting to me and I'd like to know if it has been considered before: mathoverflow.net/q/500856/17064
RT @gro_tsen: Une illustration de l'intérêt du fait que Twitter conserve les anciens tweets: pic.x.com/bmSy8xduVQ x.com/NicolasSarkozy…
I posted an answer (to an old question) on MathOverflow explaining how one can actually algorithmically compute the 27 lines on a cubic surface (by representing the lines through their Plücker coordinates): mathoverflow.net/a/500849/17064
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Lien: fr.wikipedia.org/wiki/Liste_des…
Si qqn a du temps à perdre, l'article de Wikipédia en français «Liste des îles sur la Seine» liste en gros les îles dans l'ordre amont → aval, mais bizarrement celles du département des Yvelines sont par ordre alphabétique(‽). Il faudrait corriger ça (et vérifier la liste).
RT @GenevieveMadore: Grace à son intervention musclée au téléphone en pleine nuit ce 22/09, Trump a pu stopper l'attaque conjointe de l'A…
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… Even a purely synthetic element like “nihonium” (OF COURSE you haven't heard of it; side note: even in English, I think it's silly to give such elements names, and we should stop) gets a one-character/syllable name in Chinese: ‘鉨’ (pronounced “nǐ”). 🤯 youtube.com/watch?v=8ol7Ds…
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… are named with a single syllable: ‘銪’ alone (pronounced “yǒu”) is “europium”, ‘鋱’ (pronounced “tè”) is “terbium”, and ‘鈥’ (pronounced “huǒ”) is ”holmium”. No suffix indicating “this is a chemical element” or anything. You can bet these syllables have TONS of homonyms. …
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… Chinese often likes to add a second character behind one that might otherwise suffice to denote meaning, thus increasing clarity and/or redundancy. But for some reason, for the chemical elements, it does NOT do this: even rare and obscure, or synthetic elements, …
One crazy thing I recently learned about Chinese: EVERY element in the periodic table has a name consisting of a SINGLE ideogram, and (therefore) a SINGLE syllable. This is insane considering that most Chinese words, even some very common ones, are two-syllables long: …
At least these aren't the dullest times. 😔 x.com/KyleKulinski/s…
RT @IDFmobilites: 📣 C’est officiel : le #CâbleC1, le tout 1er téléphérique d'Île-de-France, accueillera ses premiers passagers le 13 décemb…
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(L'étape suivante c'est de se demander comment se passe la formation des formateurs, et de conjecturer qu'il y a une infinité de niveaux de formation et que la place où on s'assoit dépend de la parité du niveau de formation. 🙃)
Comment ça se passe, la formation des moniteurs d'auto-école? Le formateur se met à la place de l'élève dans une voiture à double commande, et fait semblant de faire toutes sortes d'erreurs de débutant, et le moniteur en formation doit arriver à les rattraper à temps?
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A (French, white) colleague told me the following anecdote: he lived for years in Japan. On the plane going there, he thought “oh this is going to be hard: these Asian faces all look the same to me”. When returning to France, he thought “these Caucasian faces all look the same!”.
Apparently the effect that we sometimes have a hard time telling apart faces of people from other ethnic types (or ethnic types we didn't grow up around) is real and has been studied scientifically (“cross-race effect”) — it's not just casual racism: youtube.com/watch?v=RyR05m…
How Tolkien/GoT/WoT/… nerds sound to people who aren't Tolkien/GoT/WoT/… nerds: youtube.com/watch?v=atv8pf…
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Simulating a phase transition with a simple model: youtube.com/watch?v=itRV2j… — The video also includes a very clear explanation of what “temperature” and “chemical potential” are, as well as a derivation of the Boltzmann(-Gibbs) distribution law.
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On different kinds of servant jobs in a rich Victorian or Edwardian household, their hierarchy and evolution: youtube.com/watch?v=tuuDxD…
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@canard_milliard @pianocktailiste … Maintenant, on n'est pas obligé de croire Einstein: ce principe d'équivalence est nécessaire pour faire marcher sa théorie, mais ça ne le rend pas automatiquement correct: il faut tester expérimentalement. Et expérimentalement, ça marche bien: en.wikipedia.org/wiki/Equivalen…
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@canard_milliard @pianocktailiste … Contrairement à l'électromagnétisme qui agit en fonction du rapport q/m (charge sur masse) des particules, pour le gravitation, le rapport «masse gravitationnelle sur masse inertielle» doit alors toujours être le même, donc on peut le prendre égal à 1. …
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@canard_milliard @pianocktailiste Comme d'autres l'ont dit, l'explication selon Einstein c'est que la gravité n'est pas une force, c'est la courbure de l'espace-temps, et en tant que telle elle agit sur tous les objets exactement de la même manière (comme les «forces» centrifuge ou de Coriolis). …
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… Of course it's normal for everyone to believe that they're right MOST of the time. But if you can't think (and admit to yourself at least) of a recent moment when you were stubbornly defending something against valid criticism, then you're part of the problem (as we all are).
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… when watching this, everyone will probably identify with goose #1 and think “oh yes, I remember trying to convince this idiot with this obvious fact”.␤␤But we need to remember that we're ALSO goose #2 and there are far more lessons to be learned from THAT side of the story! …
An excellent short description of the psychological mechanisms (I like to point out) making most political discussions so unproductive; or: why changing other people's mind is so hard & how to try anyway: youtube.com/watch?v=Omc37T…␤␤I would like to add the following point: …
So, this @/e_cdalton “verified account” with 14.9k followers, spewing propaganda about being a “lifelong Democrat” who “just registered as a Republican”, is a bot. And there are so many more. Everything is fine. 😬 pic.x.com/LCDZqHv67M x.com/e_cdalton/stat…
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Voici un résumé que j'avais fait ici de la partie 2 en 2020: threadreaderapp.com/thread/1332447… ou directement ici: x.com/gro_tsen/statu…
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Voici le lien pour voir sur le site d'Arte: arte.tv/fr/videos/RC-0…␤␤Si vous préférez YouTube: youtube.com/watch?v=Ek9rXR… (1, “Les origines”), youtube.com/watch?v=rRp7M1… (2, “L'empreinte des civilisations”) et youtube.com/watch?v=0p32ZB… (3, “Une nouvelle ère”).
Je viens de voir qu'Arte a remis en ligne son excellent documentaire “L'odyssée de l'écriture” (sur l'histoire de l'écriture), déjà diffusé en novembre 2020. C'est vraiment très intéressant, et je recommande très vivement (surtout les deux premières parties).
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@laurentbercot Fusion cuisine is the best cuisine! 👍␤␤(It annoys the nationalists AND the prescriptivists, and it combines the best of all worlds. 😋)
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… (And the counterargument that you may have the choice of with whom to sign is a bit like saying that you sometimes get to choose which mafia boss protects you.)␤␤Now take the time to think how many contracts you ACTUALLY NEGOTIATED among those you signed.
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… If your only options are “sign” and “do not sign”, then what you have in front of you is not a freely negotiated contract — it is an ultimatum — it is blackmail. This is how losing parties are treated after a war (e.g. Germany after WW1: sign the Versailles treaty Or Else). …
Here's an important (necessary) condition to decide whether a contract is legitimate or morally defensible: did all contracting parties take an active part in negotiating its terms?␤␤Or did one party only have the options of “to sign” or “not to sign”? … x.com/gro_tsen/statu…
All license agreements say the exact same thing. They all say: “We have ALL THE RIGHTS PERMITTED BY LAW. You get NO RIGHTS EXCEPT REQUIRED BY LAW.”␤␤You didn't get to negotiate the contract, why would they give you any right they aren't legally obligated to? Of course they don't.
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@monsieurpuyo @sflicht Apparently you can cause lots of drama on social media with this kind of comment: reddit.com/r/SubredditDra… 😂
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For animals you kind of look at the whole critter to see where it belongs. For plants, you have to look at the fine details of how the petals are laid out or how the stamens are shaped or how the seeds are structured to get the family resemblance.
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… Plants keep changing their mind completely about what they look like. So hollyhocks and baobabs belong in one family (Malvaceæ), apple trees and brambles are in another (Rosaceæ), ash trees and jasmine are together (Oleaceæ), and so are lychees and maple trees (Sapindaceæ). 😣
Botanical families are weird.␤␤In zoology, you can sort of guess the family by the shape of the critter: felids are like cats, canids are like dogs, corvids are like crows, apids are like bees, and so on. There are outliers, but overall families KIND OF make sense. But plants! … x.com/gro_tsen/statu…
RT @Sadmethod: people are always saying ‘fuck cancer’, my guy was like ‘bet’ pic.x.com/7MJBLpveeA
Incidentally learning that cocoa (Theobroma genus) is part of the mallow family, which besides mallows also includes such seemingly haphazard plants as: hollyhock, cotton, durian, hibiscus, linden trees and (wait for it…) baobab. x.com/gro_tsen/statu…
RT @GenevieveMadore: gallica.bnf.fr/selections/fr/…␤Les plans par accès chronologique : du XVIᵉ au XXᵉ siècle, découvrez comment Paris s’est trans…
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Conclusions: plants can't make up their mind about which continent to grow on.
Cocoa (Theobroma cacao) is native to Central America, but the world's largest producer of cultivated cocoa (🇨🇮) is in Africa. Conversely, coffee (Coffea arabica) is native to Africa (Ethiopia), but the world's largest producer of cultivated coffee (🇧🇷) is in the Americas. 🤔
Intuitionistic logicians are excited to see the US government suddenly very keen to question the validity of double negation elimination. x.com/MixtUpMixy/sta…
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Google Maps, of course, does not disappoint: it has a label for “an island in a lake in an island in a lake in an island in a lake in Canada”… with opening hours (24 hours), reviews (averaging 4.7/5), and popular times: google.com/maps/place/An+… 😀 pic.x.com/Fv6Hi79nSN
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So apparently there's this islands in a lake on an island in a lake on an island in a lake (in Canada): openstreetmap.org/?mlat=62.65138… — and this is a record (up to arguing about what “island” and “lake” mean, of course).
The Wikipedia article on “recursive islands and lakes” looks very much like original research (and also should be named “nested” not “recursive”), but I have to admit, it's a fun topic. en.wikipedia.org/wiki/Recursive…
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Among similar lines:␤␤‣ There exists K⊆ℝ³ compact and contractible, and f:K→K continuous, yet which DOES NOT have a fixed point.␤␤‣ A counterexample is hard to find, and was only discovered in 1953: math.stackexchange.com/q/5064858/84253
I don't know which part amazes me more:␤␤‣ There exist f,g:[0,1]→[0,1] continuous, commuting (i.e. f∘g=g∘f), yet which DO NOT have a common fixed point (∄x.(x=f(x)=g(x)).␤␤‣ A counterexample is hard to find, and was only discovered in 1969: jstor.org/stable/1995330
RT @vinceflibustier: pic.x.com/0pLhi6hLDd
It's a shame we don't have a record of the Republication reaction in a parallel universe where Biden threatened to withhold federal funds from local government and universities when he didn't like the people they might elect or the things they might teach. x.com/BuzzingPop/sta…
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How the general debate week of the United Nations General Assembly functions, and how images are taken [video is in French]: youtube.com/watch?v=JNWiK6…
RT @haveigotnews: RIP Robert Redford, 1970s star of US cinema – for younger readers, a “cinema” was a large building where you went with ot…
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A lawyer tries to unwrap what US Law (and International Law) has to say about the president ordering the assassination of civilians outside of US jurisdiction: youtube.com/watch?v=7t-_m1…
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… thoughtful. Then he adds: “Why do you speak to me of the stones? It is only the arch that matters to me.”␤␤Polo replies: “Without the stones, there is no arch.”␤»␤␤— Italo Calvino, ‘Invisible Cities’ [English translation mine]
«␤Marco Polo is describing a bridge, stone by stone.␤␤“But which is the stone that supports the bridge?” asks Kublai Khan.␤␤“The bridge is not supported by this or that stone,” Marco replies, “but by the shape of the arch that they form.”␤␤Kublai Khan remains silent …
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(The 2025 pic was taken from here openstreetmap.org/?mlat=43.62333… — the 2007 pic was probably taken from about here openstreetmap.org/?mlat=43.62475… but my camera at the time didn't have a GPS receiver so I'm not exactly sure.)
Interesting to compare two pictures I took of the Toronto skyline as seen from the islands during my last two trips there: on 2007-04-17 (left) and on 2025-09-01 (right). pic.x.com/lUP0y8Rn5t x.com/gro_tsen/statu…
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(Je vais tenter de compiler un album de photos plus complet, mais ça va me prendre du temps.)
Compte-rendu sur mon blog de mon voyage avec @Conscrit_Neuneu à Toronto il y a deux semaines: madore.org/~david/weblog/… (évidemment fort long, et avec 55 notes 😅, mais on peut juste regarder quelques photos)
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… “Your joke,” replies the logician. “I finally managed to formally prove it funny.”␤␤x.com/gro_tsen/statu…
A physicist tells a joke to a logician. The logician doesn't laugh. The physicist thinks nothing of it.␤␤One month later, the physicist walks by the logician's office, and sees the logician is laughing. “What's funny?” asks the physicist. …
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I am told that the above joke has been formally certified under SMCDEL, a model checker for dynamic epistemic logic: w4eg.de/malvin/illc/sm… (click on “DrinkingLogicians”).␤␤(So now you're allowed to laugh.)
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(“Our chief weapon is antifeminism. Antifeminism and antiwokism. Our two weapons are antifeminism and antiwokism. And ruthless stalinism. Our three weapons are antifeminism and antiwokism and ruthless Stalinism. And an almost fanatical devotion to Trump. I'll come in again.”)
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(Cue three people's commissars, dressed in red, entering the room to the sound of a weird potpourri of ‘The Internationale’ and ‘The Star-Spangled Banner’ and saying: “NOBODY EXPECTS the MAGA Communists!”)
I have to admit, I did not expect the “anti-feminist, anti-queer, anti-woke, anti-environmentalist, pro-social services, pro-tax cut, pro-Donald Trump, pro-Xi Jinping, Maxist-Leninist, Stalinist, socialist patriotic MAGA Communist party”. 🤯 pic.x.com/mIDQ8UsU0M
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@JacqBens I'll grant you that my obsession with symmetry can tend to lead me astray. 😅
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@JacqBens (Or of course, the “or” could be “or, to achieve the same goal”, with same analysis as in the previous tweet. This is the most likely intention of the author, I think: “support 1 country, live in 1 country, and if mismatch, change one to align with the other, either way”.)
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@JacqBens … So my best guess was: the “or” is actually meant to be “or:” (acknowledging the two halves are equivalent), the “the” imposes uniqueness of each referent, and the overall meaning is: {supported_countries} = {residence_countries} and card(this set) = 1.
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@JacqBens … (meaning {supported_countries} ⊆ {residence_countries} or {supported_countries} ⊇ {residence_countries}). ❧ But I have a hard time giving precise meaning to “support the country you live in or live in the country you support” especially without making one half redundant. …
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@JacqBens … Here, “support a country you live in or live in a country you support” would be clear (meaning: {supported_countries} ∩ {residence_countries} ≠ ∅) albeit redundant. Also clear would be “support (all) the countries you live in or live in (all) the countries you support” …
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@JacqBens There's always much logical confusion as to what to do with a singular “the” when there isn't a unique referent (e.g., “the current king of France is bald” when there is no king: true, false or meaningless? or how about “the arrogant French guy is blond” when there are many?). …
The irony of Elon Musk reposting a tweet saying “live in the country you support” supporting a country he does not live in is only compounded by the AI-generated image supposed to represent the 🇬🇧 and showing the 🇫🇷 arc de triomphe at back. 😂␤␤[tweet id: 1966898952986591309] pic.x.com/y43f8U87fX
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@laurentbercot Cc @Conscrit_Neuneu aussi!
RT @SpencerHakimian: This is one of the funniest community notes of all time. pic.x.com/1dNM6meZDV
Le même endroit sur la route départementale 128 de l'Essonne, (à proximité de la ferme du Moulon), à Gif-sur-Yvette, photographié par Google Street View: en 2008 à gauche google.com/maps/@48.71059… versus 2025 à droite google.com/maps/@48.71059… pic.x.com/laO4SdxO11
Note that this can be used adversarially: IIUC, if you order ChatGPT to hold certain beliefs, then make it generate large amounts of computer code, put this code on GitHub, wait for the same ChatGPT model to be retrained using this code, it will pick up those beliefs. x.com/gro_tsen/statu…
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An explanation of “subliminal learning”, or how training one AI model on the output of another can pass on certain traits from student to teacher (such as: liking eagles) even though the training data seemed totally unrelated (strings of numbers): youtube.com/watch?v=NUAb6z…
RT @malonebarry: When you try to remove a piece of art and accidentally make it better. pic.x.com/PpLGuZkpyI
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@LaurentGarnier_ Ben louer une voiture en autopartage pour faire 5min de trajet entre A et B en m'évitant de me taper les bouchons depuis et vers Paris ça me paraît un bon système, oui. Mais seulement si ça marche vraiment.
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@eliaschedid Oui, c'est bien ce que je voudrais. x.com/gro_tsen/statu…
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@eliaschedid Merci, je ne savais pas. (Ceci étant, celui-là serait vraiment mauvais parce qu'il ne tient pas compte du relief.)
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Update: on me signale sur l'autre réseau qu'il y a des vélos de location Lime, mais… à Palaiseau, pas à Orsay, parce qu'il faut que la politique locale s'en mêle. Or mon point d'arrivée est à Orsay. 😖 bsky.app/profile/badbea…
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Bref, voilà ce qui illustre bien le problème de «Paris-Saclay»: non seulement c'est complètement au diable et les transports pour y aller sont merdiques, mais même pour aller d'un point à un autre DU MÊME CAMPUS, c'est mission impossible. madore.org/~david/weblog/…
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‣ Et voilà cmt on retombe fatalement sur la voiture individuelle (ou pour moi, moto). Mais je n'ai vrt pas envie de faire Paris→Palaiseau par la route demain (il va y avoir une circulation d'enfer). J'en viens à demander à ma maman (qui habite Orsay) d'emprunter sa voiture. 🙄
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… mais maintenant on me dit qu'il y a un délai de 48h pour valider le dossier. (Et je doute que ça marche tout court.) Or j'ai besoin de faire ce déplacement demain. Donc ça a l'air d'être encore une fausse route.
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… un site Web aussi cassé et dysfonctionnel. Après d'héroïques efforts j'ai réussi à envoyer les justificatifs demandés (hyper pénibles: permis recto-verso, selfie avec le permis, justificatif de domicile, bulletin de salaire, etc., tout ça depuis le mobile évidemment), …
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‣ Autopartage, à défaut? (Je veux dire, location de voiture en self-service.) Il est censé exister un truc: Clem [point] mobi. (Je suis même censé avoir droit à une réduction en tant que personnel d'un des établissements du campus.) J'ai tenté de m'inscrire: j'ai rarement vu …
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… mais je n'en vois aucun signe. Il y a peut-être des loueurs privés genre Lime. Aucun moyen de savoir sans se rendre sur place. Et quand je serai sur place, je doute de pouvoir faire une location en quelques minutes.
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‣ Vélo de loc', alors? Là aussi, ce serait l'idéal. Mais encore faut-il que ça existe! Jusqu'à preuve du contraire, je n'en sais rien. Si les pouvoirs publics étaient sérieux dans la volonté de développer Paris-Saclay, ils auraient mis en place un service PUBLIC genre Vélib, …
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‣ En vélo? Bien sûr, c'est l'idéal (ça prendrait ~10min). Mais encore faut-il avoir un vélo. Je n'en ai pas, et même si j'en avais un à moi, encore faudrait-il l'amener sur place (faire Paris→Palaiseau à vélo, pour le coup, bof).
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‣ En bus? Alors il a bien un bus (tjrs bondé) qui traverse la N118, le 91·06. Sauf que: il passe une fois tous les jamais (prévoir ~10min d'attente), il s'arrête partout (~10min pour faire le trajet), et il reste ~10min à marcher. Bilan: ~30min, à peine moins qu'à pied. 🤷
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‣ À pied? Google me dit ~45min de marche (il y a un peu plus de 3km à faire, parce qu'il y a UN SEUL point de passage au-dessus de la N118). En plus, c'est un trajet hyper désagréable à faire (longer la D128). Donc bof. 😒
Voilà qui illustre parfaitement bien les problèmes de déplacement avec le plateau de Saclay: je veux aller d'un point à un autre, SUR LE MÊME CAMPUS, qui sont distants de 1.8km à vol d'oiseau (séparés par la N118). Mais comment? ⤵️ x.com/gro_tsen/statu…
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(Pour fixer les idées, je dois aller de là openstreetmap.org/?mlat=48.71253… à là openstreetmap.org/?mlat=48.70637… — clairement un vélo serait le mieux, mais je n'en ai pas à moi.)
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⇒ Y a-t-il moyen de louer brièvement un vélo ou une voiture pour aller d'un point à l'autre du plateau?␤␤(Je n'ai pas fait gaffe pq je n'en ai jamais eu besoin, mais je crois que de tels services ont existé, et peut-être disparu, réapparu, redisparu… où en est-on maintenant?)
Question sur le plateau de Saclay:␤␤Demain je vais vouloir aller d'un point à un autre du campus (de part et d'autre de la N118). Ce serait long et chiant à faire à pied (~45min!), je n'ai pas envie de prendre la moto/voiture pour venir, et les bus sont dysfonctionnels.␤␤Donc: …
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A surprisingly interesting dive into how Soviet housing policy worked, its history, and how successive Soviet leaders created different styles in trying to lodge the ever-growing urban population: youtube.com/watch?v=Zfn8Qw…
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The history of how Chinese-language typewriters were designed and worked (before computers came along): youtube.com/watch?v=riZ5hZ…
RT @GenevieveMadore: 🤣 pic.x.com/SpgF1TuKsS
Le mouvement «bloquons tout» semble au moins avoir eu l'effet de complètement fluidifier la circulation automobile en Île-de-France: pic.x.com/lZCqwtIpcg
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@paglop2264 Mais mon point était précisément d'illustrer que le reproche qu'on fait souvent au régime parlementaire (la difficulté de former des coalitions et l'instabilité qui va avec) est complètement évitable.
Imagine you're a sunfish, minding your own business munching on jellyfish, and suddenly Kurzgesagt puts up a video just to diss you by explaining how dumb and pathetic you are: youtube.com/watch?v=gtDKKJ…␤␤(Stop the mola bullying!)
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@conazole @recherche_nom @SakumiBLR (Et bien sûr, Google ne communique pas cette information qu'ils ont extraite des panneaux, pour ne pas aider leurs concurrents.)
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@conazole @recherche_nom @SakumiBLR L'info sur Google Maps (qui, je rappelle, est maintenant la même chose que Waze) vient, que je sache, de la lecture des panneaux faite par Google lors des passages par Street View. Je ne crois pas que ce soit communiqué officiellement par la France.
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@paglop2264 “c'est ce que font la plupart des pays en Europe” → L'Allemagne peut-être (pas exactement), mais pas l'Espagne, l'Italie, la Belgique, le Royaume-Uni ni (je suis moins sûr) les Pays-Bas, et du coup ils ont une instabilité gouvernementale et/ou des coalitions longues à trouver.
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Le parlement disposerait alors de la faculté de changer le budget à tout moment… par le vote d'un budget différent, qui vaudrait jusqu'à être remplacé, etc. Sans que rien de magique ne se produise le 1er janvier (d'ailleurs, il faudrait supprimer les coupures annuelles partout).
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Le fait que le budget se vote par année est une convention comptable humaine qui n'a aucune raison sérieuse d'être maintenue. Le budget peut parfaitement être voté en renouvellement permanent jusqu'à tant qu'un autre budget soit voté.
Je rappelle aussi qu'il est parfaitement possible, et même pas spécialement compliqué, d'avoir un régime politique parlementaire dans lequel le vote du budget n'est jamais un point de blocage: il suffit de faire des budgets roulants (perpétuels) et pas par années civiles. x.com/gro_tsen/statu…
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Si on ne fait pas ça, c'est un choix. Probablement un fétichisme bizarre de l'idée que le gouvernement doit, à tout moment, disposer d'une majorité au parlement. Ce qui semble bel et bien, mais pose problème quand une telle majorité ne se constitue pas.
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Ça me semble vrt simple et naturel: le parlement élit directement le chef du gouvernement (→ un nom émerge forcément sans délai), et ne peut ensuite le renverser qu'avec une motion de censure constructive (c'est-à-dire en rassemblant une majorité autour d'une autre personne).
Je rappelle à toutes fins utiles qu'il est parfaitement possible, et même pas spécialement compliqué, d'avoir un régime politique complètement parlementaire qui évite à la fois l'instabilité gouvernementale et des longs délais pour trouver une coalition. 🧵🔽 x.com/gro_tsen/statu…
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… C'est dommage: l'histoire des progrès incrémentaux est au moins aussi importante que celle des changements soudains, et a des leçons à nous apporter, mais a tendance à être négligée parce qu'elle n'apporte pas de réponse claire («depuis quand le 🇬🇧 est-il une démocratie?»).
On m'a parlé à l'école des révolutions françaises de 1830 et 1848 et (un peu) de leurs avatars dans d'autres pays d'Europe, mais l'histoire de cmt le Royaume-Uni est devenu démocratique (ce qui ne s'est pas produit un glorieux jour en 1688 — ni en 1832) n'a jamais été abordée. … x.com/gro_tsen/statu…
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The history of the passing of the British Reform Act 1832, one of the crucial steps in making Britain incrementally more democratic, and how the country avoided going through a revolution like many other European countries did: youtube.com/watch?v=h6E4_B…
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This video sounds like it's about physics, but it's really a math/algorithmics problem: if a surface of varying height is flooded with water to a certain level, and you drain it at a point, how can we compute whether a point remains under water? youtube.com/watch?v=zzWKh8…
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@BoudonJulien @Bas_scordia C'est la légistique qui est déplorable. Si la manière dont on insère des articles sans numéroter est d'ajouter des -1, -2, -3, etc., alors les alinéas d'un article devraient systématiquement être étiquetés (a), (b), (c) pour éviter toute confusion possible.
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To this day, on social media and various messaging apps (e.g., on mobile), it is often unclear how do distinguish the two functions of “add a line break here” and “send the message now” (i.e., essentially, “return” and “enter”). GUI widget or key, we're never too sure.
A fascinating dive into the history of the key variously known as “return” or “enter” or “↵” on the keyboards of typewriters, teletypes and modern computers, and how various functions got switched around. x.com/vdesdoigts/sta…
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(Bon, en l'espèce, la mesure est sans doute soutenue par les gens qui vendent des boissons après la sécurité dans les aéroports. Dont on se demande d'ailleurs par quel loophole juridique EUX arrivent à obtenir le droit de faire passer des liquides sous prétexte de les vendre.)
Genre le coup de la limitation sur les liquides dans les avions. Ça ne sert à rien, personne de sérieux ne pense que ça sert à quoi que ce soit, mais on le fait parce qu'il faut toujours laisser les terroristes gagner en imposant des mesures pénibles de ce genre. x.com/gro_tsen/statu…
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@alexisrozen Chaque attentat terroriste a pour principal effet d'imposer à la société une mesure à la con de plus qui ne sert à rien pour la sécurité de quoi que ce soit mais permet aux politiciens de prétendre qu'ils ont fait qqch, tout en emmerdant tout le monde (=le but des terroristes).
Quand même, quelle idée géniale que les RER qui desservent l'aéroport de Paris Charles de Gaulle n'aient aucun emplacement prévu pour poser des valises.
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I think tourist shops selling Canadian merchandise (anything you can think of with a Canadian flag on it) at the airport should include a sweater with the Canadian flag and the subtext: «“a few acres of snow” (Voltaire)». 😂
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When you're famous you get a Wikipedia page. When you're very famous, your works also get their own Wikipedia page. But when you're really hyper famous, even your 4-word long quotes their own Wikipedia page!
I love how Voltaire's dismissal of Canada as “quelques arpents de neige” (“a few acres of snow”) gets to have its own Wikipedia page: en.wikipedia.org/wiki/A_few_acr… (and a long one at that!)
The guy isn't even consistent in his obloquy. x.com/NewsWire_US/st…
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Update: they are visible here google.com/maps/@43.66302… as late as 2019 on Google Street View. So I had correctly remembered the place.␤␤And I'm told they were gone in 2022: bsky.app/profile/ringbu…
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… My guess is that they were in Hart House Circle Park here: openstreetmap.org/?mlat=43.6632&… (obviously remodeled in the last <20 years) — but I'm by no means certain. Does anyone have info about when this artwork(?) was created, when it was removed, and where it was?
A question for Torontonians if there are any following me: somewhere around Queens Park there used to be four markers which precisely aligned with the top of the CN Tower, pictured below in 2007 (last time I was here). I ✺think✺ they're gone now (I couldn't find them). … pic.x.com/DOKwN9Uf5Q
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@oligomatic Yes
RT @angie_rasmussen: Vaccines are essential for controlling outbreaks. The U.S. has historically contributed significantly in this regard t… x.com/saskiapopescu/…
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@echo_pbreyer Can you post this on Bluesky so I can repost you there as well?
RT @echo_pbreyer: On this podcast, I explain the EU's #ChatControl plan: mandatory scanning of ALL private messages. This is unprecedented…
Where are we? (Difficulty 0/10) pic.x.com/sQ3al6Up63
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@fcqv For a city that has a place called “Elephant and Castle”, nothing is surprising. 😁
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The logic appears to be that the first restaurant of what would later be that chain opened (in 1954 in Toronto) in a place that just so happened to be built in the “Swiss chalet” architectural style. en.wikipedia.org/wiki/Swiss_cha…
‘Swiss Chalet’ is a Canadian restaurant chain specialized in rôtisserie chicken, even if nothing about this statement makes any bit of sense. (I don't recall Switzerland being renowned for its… chickens.) en.wikipedia.org/wiki/Swiss_Cha…
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@ColmezPierre Effectivement! x.com/gro_tsen/statu…
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It's often very hard for me to tell whether the “I can't recognize anything” feeling I have is because my memory is vague or because things have completely changed. Google Street View is immensely helpful in letting me decide (here, obviously, the latter).
The same place in Toronto's Yonge Street (around Maitland St), looking south, as imaged by Google Street View in 2009, and in 2024. google.com/maps/@43.66363… pic.x.com/usLYWtKrVw
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Here's what the map of the PATH looks like: toronto.ca/wp-content/upl… pic.x.com/nYljs6ykqw
Toronto's financial district has this vast complex network of interconnected underground shopping malls/concourses known as the “PATH”, that links many skyscrapers and subway stations together. It remains open even when the shops are closed and the whole thing is eerily empty. pic.x.com/wviwfF3bpD
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Quelqu'un comme moi qui aime avoir le choix entre plein de variantes de la même chose 🔽 ne pouvait que rester admiratif devant tant de déclinaison d'Advil. x.com/gro_tsen/statu…
Quand je pense que je vis dans un pays sous-développé où il n'y a que quelque chose comme 4 types d'Advil vendus en pharmacie. Pendant ce temps-là, au Canada: pic.x.com/jTo2nZPRqY
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@galactiknavy That would be system-wide. I don't want to contaminate system tasks (e.g. syslogd), only my personal environment.
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(Don't tell me to change the time zone from the control center or something: this would affect /etc/localtime and I want an explicit TZ environment variable so it will be passed by ssh.)
How do I set up Ubuntu (more precisely an old 20.04 Ubuntu) to add an environment variable, namely TZ=America/Toronto, to my session's environment when starting Gnome from the Gnome Display Manager?
One change I've noticed so far is that the smell of weed is everywhere. (Sale and use of cannabis was legalized in 🇨🇦 in 2018.)␤␤I'm in favor of legalizing recreational drugs like cannabis, but we need to acknowledge that, like tobacco and alcohol, there are associated nuisances. x.com/gro_tsen/statu…
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@JacqBens We had thai food in a food court in the Eaton center. And I had forgotten how large North American servings were.
Let me get this straight: Toronto opened a brand new direct train link between airport and downtown in 2015, and it runs on… diesel‽␤␤What the actual f🤯ck?
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WE'RE OUT!
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40 minutes now. This is a non negligible fraction of the total travel time.␤␤I didn't realize airport gates were such a rare commodity.
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(I think a ballpark estimate is around 300g/s, so 500kg for these 25min. Which translates to roughly 1.5 TONS of CO₂. 😱)
Plane landed 25min ago in Toronto YYZ, and we're still waiting for an available gate to disembark. 😬␤␤Meanwhile, the plane engines are running and I don't think I want to know how much kerosene they're burning per minute. 😓
RT @JohnDCook: The planets in our solar system have an average population of about one billion.
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@JacqBens So if I want the size (i.e. ~128GB, definitely <1TB) and form factor of a USB thumb drive and reliability/speed of an SSD, at an intermediate price, I'm just out of luck?
Why is the read-write performance of USB thumb drives so much worse than that of an SSD drive in a USB case: aren't the two supposed to be more or less equivalent?␤␤Also, why don't USB thumb drives support “trim”?
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@JacqBens Yes. Basically it takes two computers (or two dirs on the same computer), each with a copy of a bunch of files, and makes sure the target's copy matches the source's, without transferring everything. But it has LOTS of bells and whistles.
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Anyone old enough to remember how horrible it was to keep track of files and backups before rsync (when we only had rdist or not even that) will join me in wishing the rsync developers all the blessings that this world can bestow upon them.
One thoroughly underappreciated computer program which made my life oh so much easier is rsync.␤␤Every time I move around lots of files between backups and backups of backups and stuff like that, I pause to ponder how much rsync has made my life easier.
RT @SaarelaHC: Highland Cattle photo of the day pic.x.com/UQIopRfQqC
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Also closed since 2007: the ‘Science City’ shop that used to be in the Holt Renfrew Centre and whose gadgets I loved as a kid; and the ‘World's Biggest Bookstore’ that used to be on 20 Edward St.␤␤(Δὶς ἐς τὸν αὐτὸν ποταμὸν οὐκ ἂν ἐμβαίης. 😔)
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Sadly, I already know this: the Ontario Science Centre, which was one of my favorite places when I lived in Toronto in 1984–1985, is permanently closed (already in 2007 it had switched from showing instructive science exhibits to mostly just being fun for kids).
Last time I was in Toronto was 18 years ago. What major changes should I look for in the city as I go back?
Very concerning: Google announces steps (under pretense of “security”) to bring Android closer to Apple's iOS level of vendor locking by preventing users from installing apps they want: arstechnica.com/gadgets/2025/0… — Will likely break F-Droid and with it the Android FOSS ecosystem.
Je pense que les plantes sont plus dissuasives que le panneau «interdit à tout véhicule à moteur», là: google.com/maps/@48.40777… pic.x.com/Zc6P7YiEoG
RT @alexkrokus: this one was apparently a big hit among librarians pic.x.com/w0IQWcgRSl x.com/cybrid101/stat…
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@pianocktailiste Comme je le faisais remarquer naguère, l'obsession pour la symétrie, ce n'est pas tant un truc de matheux ou de physicien que de mystique, en fait. madore.org/~david/weblog/…
Toujours un plaisir d'y manger. 😋 pic.x.com/AiW3Vu7MUU x.com/gro_tsen/statu…
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Note that hypotheses are crucial: if f:ℝ→ℝ is assumed to be continuous ✵everywhere✵, differentiable ✵almost everywhere✵ and satisfy f′≥0 ✵a.e.✵, then f can fail to be nondecreasing (consider the negative of a “Devil's staircase” Cantor function). en.wikipedia.org/wiki/Cantor_fu…
An often overlooked theorem: if a function f:ℝ→ℝ is differentiable ✵everywhere✵ and f′≥0 ✵almost everywhere✵, then in fact f is monotonic (“nondecreasing”) and f′≥0 everywhere. mathoverflow.net/a/499465/17064
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@pianocktailiste @drmtgr C'est le passage qui commence par «Et le comportement asymptotique est peut-être plus intuitif» dans mon billet, ça. 😉 Mais cette formule ne peut pas être exacte, ne serait-ce que parce qu'elle n'est pas symétrique p ↦ 1−p.
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An interesting account of the neurology of mathematics, and how mathematicians make use of specific areas of their brains to understand mathematical statements (not the general language areas), which seem involved in logical thinking: youtube.com/watch?v=E_EanZ…
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@pianocktailiste @drmtgr (It's pretty clear when you think of an extreme violation where A always beats B who always beats C who always beats A: you can easily use this to transfer points from any player to any other player by setting up games in the way that favors whom you want to favor.)
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@pianocktailiste @drmtgr … As to what happens if this assumption is NOT satisfied, well the Elo rankings will converge differently according to how the games are played, and (I think) you can use the discrepancy to manipulate scores by running games in one or another way.
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@pianocktailiste @drmtgr … This is something that is susceptible to experimental test, but I don't know of any such test has been made. Initially Elo had proposed a Gaussian model, then switched to logistic, so there doesn't seem to be a really deep reasoning behind it. …
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@pianocktailiste @drmtgr I want to emphasize that Elo's logistic model makes a very specific assumption about winning probabilities: that if Alice wins over Bob with probability p and Bob wins over Charlie with probability q, then Alice wins over Charlie with probability p·q/(1−p−q+2p·q). …
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@pianocktailiste @drmtgr I have, indeed, already thought about this: madore.org/~david/weblog/… 😅
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Blåhaj (the Ikea shark plushie) goes to waffle house at 3AM and havoc ensues: youtube.com/watch?v=X1beEu… I don't know exactly what I expected when I clicked on that animation short, but it was much better. 😂
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… And the puzzles are also a metaphor for the novel itself, which is itself divided in pieces which the reader can reassemble in various ways.
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‘Life: A User's Manual’ (‘La Vie mode d'emploi’, possibly my favorite novel) is the story of a fictional Parisian building and various mysteries around its inhabitants; and the central story involves a guy who is obsessed with jigsaw puzzles. …
Currently watching ‘Only Murders in the Building’ S02E07, and we learn that Mabel loves jigsaw puzzles and see her trying to solve one showing the characters in the building. This HAS to be a reference to G. Perec's novel ‘Life: A User's Manual’, right? Or am I imagining things?
J'ai parlé de métaphysique sur mon blog, et je n'aurais sans doute pas dû. En tout cas, c'est long et chiant. madore.org/~david/weblog/…
Le pigeonnier du parc de Choisy (Paris 13) a une boîte aux lettres, donc si vous voulez écrire aux pigeons vous savez comment faire. pic.x.com/jxkWtoogtS
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@robert_barny Néanmoins c'est standard pour la mesure d'espérance de vie, même si c'est artificiel.
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@robert_barny Mais c'est pire que ça: le taux de mortalité par âge est supposé égal à celui de la periode de statistiques (ici, 2012–2018 je crois), or c'est impossible: personne ne peut avoir 10 ans et 60 ans dans la même periode.
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@robert_barny Ce sont des données synthétiques: on mesure la mortalité par âge, sexe et niveau de revenus, et on publie les données sous forme de survie de cohortes ayant ce taux de mortalité. Donc l'hypothèse est que le vingtile ne change pas.
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@robert_barny Je devine qqch comme: le plus important facteur de la surmortalité des plus défavorisés, c'est qu'ils ont un travail plus fatigant ou dangereux, et cet effet s'estompe à la retraite.
I asked a question on MathOverflow about probability distributions that ensures that the probability of the “who dies first?” question depends only on the age difference (and not the ages themselves). mathoverflow.net/q/499369/17064 x.com/gro_tsen/statu…
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Et comme l'INSEE fournit aussi des données par niveaux de revenus, je peux également faire des graphiques montrant la différence de survie entre le vingtile le plus pauvre (v01) et le vingtile le plus riche (v20): ⬇️ pic.x.com/qNnSdc5SFj
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Comme on me le fait remarquer, c'est plus clair avec des guides autour de la diagonale (j'ai mis y=x en plein et aussi y = x ± 5ans en pointillés): ⬇️ pic.x.com/cWXOv1jdGh
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PS: Désolé pour l'utilisation du symbole ‘♁’ au lieu de ‘♀︎’ (je m'attendais à ce qu'ils soient adjacents dans Unicode, mais évidemment il y a la Terre entre Vénus et Mars). Pas la peine de refaire le fil pour ça, je pense.
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Ceci étant, quand on regarde de plus près, le graphe ♂/♂ et le graphe ♀/♀ ne sont pas rigoureusement identiques, p.ex. les bandes d'équi-probabilité sont plus resserrées autour de la diagonale sur le graphe ♀/♀ que sur le graphe ♂/♂. Je ne sais pas bien comment expliquer.
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Pareil, la différence de sexe équivaut à 4–6 ans de différence d'âge, quel que soit l'âge. Ça diminue à peine: en gros c'est 6 ans à la naissance, 5 ans à 50 ans, 4 ans à 80 ans.
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Autrement dit, je pensais voir les bandes équi-proba s'écarter ou se rapprocher de la diagonale, mais en fait, presque pas. La proba de survie favorise plus la personne plus jeune quand les deux personnes vieillissent (à différence d'âge constante), mais pas énormément.
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Je m'attendais bien sûr à ce que la proba dépende de la différence d'âge (duh…), mais je ne m'attendais pas, en fait, à ce que la proba ne dépende quasiment QUE de ça (pour une combinaison de sexes donnée). Je pensais que ça varierait avec l'âge.
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Et le script Perl que j'ai utilisé pour faire les calculs est là: gist.github.com/Gro-Tsen/e7540… (je donne en commentaire la ligne de commande Gnuplot utilisée pour produire les graphiques).
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La source des données est là: insee.fr/fr/statistique… (INSEE, “Tables de mortalité par sexe, âge et niveau de vie”; j'ai utilisé les valeurs de la colonne C, lignes 9–113, des feuilles 1 et 2, comme source pour mes graphiques).
Graphiques pas très drôles: on a deux personnes en France, d'âges x et y. D'après les tableaux de mortalité de l'INSEE, quelle est la probabilité que la personne d'âge x survive à la personne d'âge y? Trois graphiques, un pour chaque combinaison de sexes. Qqs remarques. 🧵⤵️ pic.x.com/7jejHSrITy
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@robert_barny … ce qui peut amener à ce qu'une fausse identification soit de plus en plus souvent proposée et confirmée? je ne sais pas s'ils ont un mécanisme pour éviter ce phénomène).
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@robert_barny … Ceci dit, ça ne marche que si la base de connaissances est fiable, et je m'interroge pour celle de PlantNet (est-ce qu'il n'y a pas plein de gens qui, voyant que l'app leur identifie une espèce au moins plausible, se disent «oui, ça semble crédible» et confirment, …
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@robert_barny En effet, c'est le genre de choses pour lesquelles des techniques floues (qu'on peut regrouper sous le terme d'«IA») donnent de meilleurs résultats qu'un système de décision fixe fondé sur des critères rigides (choisis pour être discriminants, donc pas évidents à voir). …
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@robert_barny Je considère surtout que le terme «IA» ne veut rien dire du tout tellement il recouvre des techniques distinctes qui ont été mises ensemble pour des raisons essentiellement de marketing. Mais pourquoi cette question?
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@robert_barny J'utilise PlantNet (enfin, pour ce genre de plantes; pour les arbres de Paris, j'utilise la base de données opendata.paris.fr/explore/datase… ).
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Ici (rue de la Fontaine à Mulard), la ville de Paris nous promet qu'ils vont planter des choses, mais qqs plantes aventurières n'ont pas attendu, comme ces Onopordum acanthium qui font de magnifiques fleurs magenta. J'ai peur qu'on les détruise pour les occupants «officiels». pic.x.com/PRm46bTQFh
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Ça me désole, ce sont des arbres que j'aime beaucoup. Et on comprend encore mal cette maladie qui parasite leurs feuilles et les leur font perdre plus d'un mois en avance.
Nous sommes le 19 août, mais les marronniers¹ parisiens sont tellement malades que pour eux c'est déjà l'automne et le moment de perdre leurs feuilles.␤␤1. Aesculus hippocastanum pic.x.com/eNZmpfosI4
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… not to treat them like children who must be restricted for their own safety. So anyway, I hope this mini-tutorial on how to disable HSTS in Firefox for a specific site is useful. Of course, you should only do this if you understand what this means and entails. ❦ •11/11
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… this is truly “I'm afraid I can't do that, Dave” territory. I'm supposed to be the boss, not my browser! The point of Free Software is to empower users, even let them shoot themselves in the foot if they so require (warning them about it is good, though!), … •10/11
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… because there are sites for which HSTS makes some kind of sense, and you should at least be given a warning before disabling it. ❧ Anyway, I just hate this paternalistic “you can't add an exception to visit this site” and “there is nothing you can do” tone: … •9/11
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After editing this file (with the browser not running!) just restart Firefox and visit the site: this time it should let you set an exception. So it's actually pretty simple. You can also just delete the “SiteSecurityServiceState.bin” file, but I wouldn't recommend this … •8/11
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… just replace it with a date in the past (in my case it was 1766307067639 meaning 2025-12-21T08:51:07.639Z, and I replaced it with 1000000000000 meaning 2001-09-09T01:46:40Z, because that's easy to type; maybe going too far back might have caused problems, I don't know). •7/11
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… search for the domain name that you want to remove HSTS for, then go forward approximately 0x100 = 256 bytes in the file where there is a number, written in decimal (in text), which is a Unix timestamp in milliseconds. This is when this HSTS entry is set to expire: … •6/11
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… this doesn't really matter because it's pretty trivial anyway. So if you encounter an HSTS error and you want to add a security exception that Firefox won't let you add, open a binary editor on the “SiteSecurityServiceState.bin” file in your profile, … •5/11
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… but the current relevant location (as of 2025-08) is “SiteSecurityServiceState.bin”: this is where Firefox stores the information of which domains requested HTTP Strict Transport Security (HSTS) and until when. It's a binary file and its format is undocumented. But! … •4/11
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But of course, Firefox must store the information “this site has requested HSTS” somewhere in the user's profile. But where? Mozilla, as usual, changed its mind several times around it: it was in “permissions.sqlite”, then it moved to “SiteSecurityServiceState.txt”, … •3/11
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So, basically, what HSTS does is tell the browser “next time you connect to this site (and until such date in the future)”, do it with HTTPS only, and don't allow a security bypass. This makes sense for a banking site, certainly not for a webcomic! •2/11 developer.mozilla.org/en-US/docs/Web…
One week later, another bullsh💩t security warning in a webcomic I read daily. (Take that, people who claim such errors are rare!) This time, Firefox won't let me add an exception because of HTTP Strict Transport Security (HSTS). So I found out how to do it anyway. 🧵⤵️ •1/11 pic.x.com/UWMdLLbmQi x.com/gro_tsen/statu…
@laurentbercot If I remember your past hobbies correctly, you may be interested in this: projectaon.org/en/Main/Books (the Joe Dever ‘Lone Wolf’ gamebooks and miscellaneous related material)
RT @haveigotnews: Donald Trump's leadership on Ukraine explained:␤␤- November: "I will end the war within 24 hours of becoming President"…
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@JeanDellass @LonardJulien3 @cortisquared … PS: j'avais fait cette vidéo il y a longtemps, qui illustre bien les compromis de diverses projections (ici toutes azimutales, donc il n'y a pas Mercator dedans, mais il y a la stéréographique qui est aussi conforme): youtube.com/watch?v=LKcTbI…
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@JeanDellass @LonardJulien3 @cortisquared … (Bon, en fait, Web Mercator n'est pas vraiment conforme, parce que la Terre n'est pas une sphère mais un ellipsoïde oblate, et que Web Mercator utilise, bêtement, la latitude géographique au lieu de la latitude conforme. Mais l'écart d'échelles n'est pas très important.) …
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@JeanDellass @LonardJulien3 @cortisquared … juste de la latitude (par une fonction pas hyper compliquée). Et si on tronque un peu les régions polaires, ça tient pile dans un carré. C'est pour ça que ça a été adopté dans le standard «Web Mercator» en.wikipedia.org/wiki/Web_Merca… utilisé par exemple par OpenStreetMap. …
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@JeanDellass @LonardJulien3 @cortisquared … Maintenant, Mercator n'est pas la seule projection conforme (la projection stéréographique, qu'on peut centrer en le point qu'on choisit, est peut-être plus sympa). Mais elle a l'avantage d'être hyper simple: l'abscisse est juste la longitude, l'ordonnée dépend …
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@JeanDellass @LonardJulien3 @cortisquared … Et si on veut faire une carte interactive zoomable, cette propriété est absolument indispensable, parce que si on a une distortion locale des formes (échelle différente selon la direction), on a beau zoomer autant qu'on veut, elle ne disparaîtra jamais. …
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@JeanDellass @LonardJulien3 @cortisquared Sur le fond, je dirais que l'intérêt d'une projection conforme, ce n'est pas juste qu'elle préserve les ✵angles✵ que qu'elle préserve les ✵formes✵: en chaque point, il y a une seule échelle, qui est la même dans toute les directions (même si elle varie selon le point). …
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… Parce que moi ça m'arrive assez souvent (enfin, je crois que ce sont des guêpes à la couleur de la trace que ça laisse), et le bruit que ça fait contre le casque ou le blouson ne me donnent pas envie de savoir l'effet sur la peau nue.
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… Et c'est une chose de se dire qu'on est invulnérable et qu'on ne va pas se raper la peau contre le bitume à 80km/h, mais même sans penser à ça: ces gens n'entrent jamais en collision avec une guêpe? …
J'ai vraiment du mal à comprendre comment des gens peuvent rouler à moto en tee-shirt. OK, il fait chaud, c'est pas agréable de porter un blouson en cuir (mais il y en a en mesh — ou en cuir perforé — qui sont bien ventilés donc très supportables quand on roule). …
So, I stumbled upon these manga-style illustrations made by Yuki Akimoto (秋本 祐希) of the particles in the standard model of particle physics, and I thought they were too cute not to share. higgstan.com/particle-image/ pic.x.com/P3eRlaM5qO
RT @captgouda24: How costly are poorly written laws? A team of Italian researchers argue that the drafting of Italy’s laws alone costs them…
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Ou encore ces différentes planplantes qui essaient vaillamment de se faire un petit espace pour vivre dans l'interstice entre un immeuble et un trottoir, et que les services de la ville de Paris viennent régulièrement occire. (La plus grande ici est une Erigeron sumatrensis.) pic.x.com/ogEoAZv8t8
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@EleuEThana J'ai eu la même idée: x.com/gro_tsen/statu…
J'ai une tendresse particulière pour les plantes que personne n'a plantées («mauvaises herbes») qui décident toutes seules de s'installer dans un petit coin de terre. La jardinière de notre cuisine accueille au moins une graminée (Setaria pumila?), une violette et une bryophyte. pic.x.com/qyBzxMe8eH
RT @signalapp: mastodon.social/@aboutsignal/1…
Il faut reconnaître à Google Street View un niveau assez impressionnant de ténacité et de persévérance quand ils en arrivent à passer photographier même des routes aussi fréquentées que ça: google.com/maps/@48.32983… pic.x.com/UAlIfygvTM
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@JacqBens Pour l'instant, l'hypothèse la plus probable que je trouve, c'est une cotisation qui serait calculée sur une base annuelle, et dont on paierait chaque mois 1/12 de ce qui reste à payer, arrondi au centime. Bizarre, mais pas impossible.
RT @BoosGarden43: pic.x.com/fHkeqtIVrs
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@laurentbercot This isn't even remotely related to what I was saying.
Si j'essaie de comprendre pourquoi mes salaires nets de juin 2025 et juillet 2025 diffèrent par exactement 1 CENTIME (dans une ligne intitulée «COT SAL RAFP»), est-ce que je vais le regretter? 🤔
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@shpostx @Grogro18985296 Il est cité en 19/21 du fil: madore.org/~david/weblog/…
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@France3Paris @UnivParisSaclay @ShanghaiRanking 😩 Chaque année, le 15 août, paraît le «classement de Shanghaï», des services de comm' imbéciles se gargarisent de leur place, et il faut réexpliquer pourquoi ce classement ne veut rien dire et qu'il est même nuisible d'en parler et de le regarder. 🧵🔽 x.com/gro_tsen/statu…
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… amène à exiler des milliers d'étudiants et d'enseignants-chercheurs sur un «campus» à Triffouilly-lès-Saclay qui ne dispose d'aucun transport en commun décent, absurdité écologique et humaine, juste pour promouvoir l'affichage d'une marque (⬇️). Pas de quoi se vanter! •21/21 pic.x.com/KXPfopiAd9
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Donc voilà, le classement de Shanghaï encourage ce pilotage complètement absurde de l'ESR qui enfouit les enseignants-chercheurs sous la bureaucratie de tonnes de coquilles administratives inutiles, les pousse à concourir plutôt que coopérer les uns avec les autres, et … •20/21
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Et «Paris-Saclay», c'est un projet complètement absurde de réunir toutes sortes d'entités disparates au même endroit sous un même nom qui est un pur mensonge. Là aussi, j'en ai parlé sur mon blog madore.org/~david/weblog/… donc je n'insiste pas plus. •19/21
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… regrouper toutes sortes d'établissement pour faire croire au classement de Shanghaï (et autres classements du même acabit) que c'est une seule entité, tout en ménageant les petits chefs locaux de chacune des entités «fusionnées». •18/21
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… de rapprochement, de regroupement ou de fusion des établissements d'enseignement supérieur et de recherche» (oui, c'est long à dire!). Ce nom à rallonge incompréhensible résulte justement d'un laborieux compromis entre fusion et non-fusion: … •17/21
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L'Université Paris-Saclay n'est pas une université: c'est un «établissement public à caractère scientifique, culturel et professionnel expérimental prévu à l'article 1er de l'ordonnance nº2018-1131 du 12 décembre 2018 relative à l'expérimentation de nouvelles formes … •16/21
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Et justement, rien de mieux pour illustrer cette manie des fusions absurdes que l'«Université Paris-Saclay», dont je rappelle qu'elle n'est ni une université, ni à Paris, ni à Saclay. Ce doublespeak s'explique précisément par cette course aux fusions. •15/21
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Je ne saurais mieux décrire cette manie des fusion que cette hilarante nouvelle satirique pseudonyme, “Fusion et confusion” (de la série “Dessous de paillasse” par Élodie Sabin-Teyssier): dessous-de-paillasse.salle-s.org/Fusion_et_conf… — c'est hilarant et tellement vrai! •14/21
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De cette idiosyncrasie méthodologique du classement de Shanghaï est née une «course à la fusion» où on réunit des institutions simplement pour essayer de persuader le classement de les compter comme une seule entité. Ce qui accroît la bureaucratie et l'énergie perdue. •13/21
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… sans diviser par la taille de l'institution. (En physique, on dirait que c'est une mesure «extensive», pas «intensive».) Donc juste en augmentant la TAILLE des institutions, on fait forcément monter leur place dans le classement. •12/21
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Le problème méthodologique, c'est qu'en plus, le classement de Shanghaï compte toutes sortes de bons points (prix Nobel, publications, toutes sortes de trucs choisis un peu arbitrairement) et se contente de les sommer pour chaque institution, … •11/21
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Donc, en soi, les classements de ce genre sont une manière de détruire le climat de confiance et de coopération inter-institutions nécessaire au bon fonctionnement de la recherche scientifique. (J'en ai parlé dans mon blog madore.org/~david/weblog/… — je n'insiste pas.) •10/21
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Le pb structurel, c'est que la science est par nature une activité coopératrice. N'importe quel classement de ce genre la transforme en compétition, dc fait perdre une productivité immense à la recherche à tenter de faire mieux que les voisins au lieu de coopérer avec eux. •9/21
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Il y a au moins deux problèmes fondamentaux dans le classement de Shanghaï, qui expliquent les dommages qu'il fait (surtout en France, donc). L'un est structurel, l'autre est méthodologique. •8/21
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En fait c'est surtout en 🇫🇷 que ça a eu cet effet. Je ne dis pas que le classement de Shanghaï est ignoré (comme il mérite de l'être!) dans tout autre pays, mais les politiques et dirigeants de l'ESR français y accordent une attention qui ont conduit à des dégâts immenses. •7/21
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Je veux dire que ✺SI✺ la Chine avait eu la volonté de casser le fonctionnement de la recherche d'autres pays (notamment 🇫🇷) en l'obligeant à des restructurations absurdes et une course à la médaille qu'ELLE (la 🇨🇳) décerne, elle ne s'y serait pas mieux prise autrement. •6/21
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Et je ne dis pas forcément que c'était une volonté délibérée d'empoisonner le monde universitaire non-chinois en le forçant à adopter des critères de classement faits par la Chine et adaptés pour la Chine. Je ne crois pas. Mais c'est le résultat que ça eu en pratique. •5/21
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Je ne dis pas forcément que c'était l'intention (initiale): à la base, ce classement est un outil interne développé par l'université Jiāotōng de Shanghaï (et qui relève peut-être de politique interne, p.ex., pour se démarquer de l'université de Pékin — je n'en sais rien). •4/21
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… ce que je veux dire par là, c'est que même si la Chine ne se place pas elle-même en premier de ce classement, l'attention portée à ce classement promeut les critères que la Chine veut voir utilisés pour évaluer le monde universitaire. (À commencer par la taille.) •3/21
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Commençons par l'évidence: le but de ce classement est de mesurer les critères que les autorités chinoises considèrent comme utiles pour piloter le fonctionnement de leur système universitaire. Ce n'est pas exactement neutre: … •2/21
😩 Chaque année, le 15 août, paraît le «classement de Shanghaï», des services de comm' imbéciles se gargarisent de leur place, et chaque année je dois réexpliquer pourquoi ce classement ne veut rien dire et qu'il est même nuisible d'en parler et de le regarder. •1/21 🧵⤵️ pic.x.com/lPCgMsoE2l x.com/France3Paris/s…
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@jjvie Alors je suis peut-être taquin en parlant de distance à vol d'oiseau, mais en ligne droite je trouve:␤⁃ Le Guichet: 2.14km␤⁃ Orsay-Ville: 2.03km␤⁃ Bures-sur-Yvette: 1.87km␤⁃ La Hacquinière: 2.18km␤⁃ Gif-sur-Yvette: 2.64km
Anyone explaining that “fascism rose because of X” (with X = some clear identifiable cause or theme), like “Rome fell because of X”, is essentially just using the fallacy of historical determinism to reflect their own preoccupations regarding present human affairs.
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@canard_milliard @SakumiBLR @VaeVix @moreau1_quentin Il me semble vaguement qu'à mon époque certains des physiciens (ou chimistes?) préparant l'agreg avaient vraiment des cours à Montrouge. Mais ça date, et je ne suis plus sûr.␤␤Il y a peut-être même (eu) des choses à Foljuif.
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@Hzdni L'ENS de Saint-Cloud a fusionné avec celle de Fontenay, puis une partie a déménagé à Lyon (→ ENS de Lyon), puis une autre partie à déménagé à Lyon (→ ENS Lettres et Sciences Humaines), puis les deux parties ont refusionné et c'est maintenant l'ENS de Lyon.␤␤Faut suivre!
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… et l'arrêt de RER le plus proche est celui de Bures-sur-Yvette.␤␤Ce qui est bien avec l'enseignement supérieur français, c'est que les choses sont claires, simples et lisibles.
#ClubContexte L'École Normale Supérieure de Paris-Saclay (à ne pas confondre avec l'École Normale Supérieure, ou «Ulm», qui est à Paris pas à Ulm) est l'ancienne École Normale Supérieure de Cachan qui a déménagé: elle n'est située ni à Paris, ni à Saclay, mais à Gif-sur-Yvette …
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@maraevantree Maybe… try giving some context explaining what it is you're talking about?
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The reason this is (slightly) surprising is that it goes against my (slightly prejudiced) idea that people who study mathematical games for economics don't really talk much with those who study mathematical games for logic or combinatorics.
I only just realized that the “Gale” of the Gale-Shapley algorithm (for stable marriages) is the same as the one of Gale-Stewart perfect information games (as in open determinacy), viꝫ. David Gale of UC Berkeley.
Apparently the “Pebble” e-paper smartwatch is back, and the OS is now open source: repebble.com
RT @cnlohr: pic.x.com/zHdo63uZ73
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… the answer can be produced using them.␤␤This thought is inspired by the following related ‘Ars Technica’ article, pointing out that it makes no sense to ask LLMs to comment on their mistakes: arstechnica.com/ai/2025/08/why…
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… Because remember, they generate text sequentially. If you get the answer first, following explanations will be an ex post facto reconstruction based on previous text and in no way a justification of how the AI “got there”. By contrast, if you ask for explanations first, …
This fact should be obvious to anyone who understands even a little bit about how they work, but:␤␤👉 If you're going to ask a question to a Large Language Model AI and ask for explanations, always ask it to produce the explanations/reasoning FIRST and the answer AFTER.␤␤…
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@Jilcaesel A final thought: even just politically, the fall of the WRE is implicitly presented as a bad thing — but why should we accept this narrative? Why is a centrifugal displacement of power bad? (There was violence, of course, but it's unclear whether it's the cause or the effect.)
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@Jilcaesel … the sack in question, so it's not like the debate is new.) And indeed you can make the point that Christianity replaced the temporal structure of the Roman empire by a spiritual one, so by focusing on the temporal you are begging the question.
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@Jilcaesel … with Christianity: Augustine wrote his most famous work (‘The City of God’) to argue that the sack of rome of 410 did not matter because what mattered was the City of God, not that of Man. (And also that Christianity was not responsible for …
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@Jilcaesel Let me put it differently: whether the fall of the WRE matters is probably more a reflection of our own views on what we should be looking at in History (political structure, economics, ethnosociology, etc.) than some objective reality. And maybe THAT has a lot to do …
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@Jilcaesel … if this disappearance represents a change of a more different nature in the evolution of societies around the Mediterranean than the evolutions that they had already undergone and would yet undergo (until the appearance of feudalism, say).
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@Jilcaesel … (Of course it depends where you look at it. In Britain it was certainly hugely important. In Italy and Gaul, probably far less.) I mean, I don't deny that something that we can call the “Western Roman Empire” ceased to exist, but I don't know …
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@Jilcaesel … And so on. Italy was reconquered by the (Eastern) Roman empire, and then lost again, and a new Roman empire was founded in 800. Politically, the relation between local powers and central ones changed many times. I'm not convinced the 450–500 period was so different. …
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@Jilcaesel But even that is dubious! Certainly things changed between 450 and 500, but they also changed between 400 and 450 (the sack of Rome in 410 had certainly been seen as important by contemporaries, unlike 476), and also between 350 and 400, or between 500 and 550. …
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@Jilcaesel Unlike in Asimov's SF retelling of things (largely influenced by Gibbon), which might have impacted your way of imagining things, and certainly did mine, the “fall of the Empire” did not represent a major political, cultural, economic or sociological breaking point in the West.
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@Jilcaesel … some kind of “spinoff”: they were very much Romans and considered themselves as such. The idea that “the Roman Empire fell in 476”, while of course not entirely false, is largely the result of an ex post facto retelling of events, of which Edward Gibbon is a major figure.
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@Jilcaesel I'm not a historian, but many actual historians I've read or listened to on the subject were very clear on the fact that ⓐthe “fall” of the WRE in 476CE is a somewhat arbitrary date that was hardly even noticed by contemporaries, and ⓑthe Byzantine empire was not …
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@pbeyssac @ordrespontane Et ne parlons pas des ondes demi-micrométriques! Ces proches parentes des UV provoquent des modifications du comportement humain et des troubles du sommeil, et sont émises en grande quantité par les LEDs que nous installons partout. À bannir! x.com/ngspiensfr/sta…
RT @ngspiensfr: @ChampoDr Les nouveaux éclairages, lampes fluocompactes et à LED, émettent énormément d'ondes demi-micrométriques.␤Les onde…
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This shit happens ALL THE TIME.␤␤So of course ppl must be getting used to adding security exceptions ALL THE TIME. Thereby negating the security that HTTPS is supposed to bring. Which, again, makes sense for sites with actual confidential data or trust at stake — not webcomics!
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“But!” you say, “it's not that bad: all you have to do is click on ‘advanced’ and add an exception.”␤␤No: this ↙️ is what I get once I do this. No images are visible because they are from a different subdomain, “static.existentialcomics.com”. (This ↘️ is what it should look like.) pic.x.com/DcA4lKbztm
Once again, thanks to HTTPS and ‘Let's Encrypt’'s policy of rapidly expiring certificates (why do certificates need to expire? nobody knows!) for protecting me from… <checks notes> …reading a webcomic.␤␤(Who knows? I might have read a <shudder> impostor comic!) pic.x.com/7Nw4OXK4W5
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@Jilcaesel OK, I don't think it was particularly cleverly worded, but if you acknowledge it was a troll, that's a fair point.
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@Jilcaesel … Now admittedly you can't read this person's mind, but you can read your own: what was your reason for retweeting him? What point are you trying to underline re Rome and Christianity? Surely there must be one.
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@Jilcaesel I'm sorry, but in a good faith discussion one does not make claims that are deliberately worded to be confusing, ambiguous or otherwise misleading in order too fool the people one is discussing with, who, incidentally, are not enemies. …
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@Jilcaesel Yeah, so pretty much textbook motte and bailey fallacy.
RT @DrCassos: Dans cette situation, je :␤␤A) fonce droit dans le mur (mon père avait raison)␤B) prends un vélib et je laisse la voiture là…
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@chrsnjk It is often said that rome fell in 476. This only refers to the Western Roman Empire (of which Rome wasn't even the capital any more), and even then it's a somewhat arbitrary limit. The Eastern Roman Empire fell in 1453, and that too is a simplification.
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@Jilcaesel I.e., a motte and bailey fallacy: making sure everyone will understand something but, if pressed about it, claiming it wasn't what he meant. So exactly what nontrivial point was he trying to make re Rome and Christianity?
RT @BallouxFrancois: We uncovered a surprisingly high prevalence of fungal taxa -- including Candida and Aspergillus spp. -- in approximate…
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Basically anyone who claims “Rome fell because of X” is an idiot¹ and should be ignored.␤␤1. And did you know? Rome fell because of idiots of this kind! 😉
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Seriously, I don't want to defend the idiots ascribing the fall of Rome to depravity, liberalization of mores, racial mingling or any such stupid idea, but to claim it was due to Christianity is equally stupid. That was novel when Gibbon did it in the 1780's — no longer.
I'm sorry, but the Roman empire fell in 1453, and by that time Nicene Christianity had been the official religion of the empire for over 1000 years, just about as long as it had been pagan before. x.com/thecaptain_nem…
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x.com/gro_tsen/statu…
Arrêtez tout! Je viens de découvrir qu'il y a une nouvelle saison (3) de la série documentaire “Quand l'Histoire fait dates” de Patrick Boucheron. Et les deux saisons précédentes sont de nouveau disponibles. Je suis complètement fan de cette série. arte.tv/fr/videos/RC-0…
RT @ngspiensfr: @RokonVR @FFmpeg To learn programming, learn with several programming languages, as different from each other as possible.
Chevreuil (Capreolus capreolus) vu il y a peu dans la forêt des Fausses Reposes, Marnes-la-Coquette (Hauts-de-Seine).␤␤(Il est au centre de l'image. J'aurais voulu zoomer pour le prendre mieux, mais le temps que je fasse ça, il avait détalé.) pic.x.com/eLslDu2UWa
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@JacqBens 😅 And here I was, so pure and innocent, completely oblivious to the double entendre.␤␤(Seriously, though, he clarified “AI, the program” — and I certainly didn't want to argue that there's more than one program. Of course, it might still have been a pickup attempt!)
Ce qui est rigolo avec ce genre de relevés GPS avec courbe de vitesse¹, c'est qu'on voit parfaitement sous forme de plateaux horizontaux de la courbe les moments où j'ai utilisé le régulateur de vitesse de la moto.␤␤1. Ici produit par le programme “GPXSee”. pic.x.com/QTm9D478h1
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La Roche-Guyon (Val-d'Oise), il y a environ 1h30 pic.x.com/weYJN7SMvT
Jardin zen du centre hospitalier du Vexin (“sanatorium d'Aincourt”, partiellement abandonné), Aincourt, Val-d'Oise. pic.x.com/A2fGIU82X8
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Now at this point I ✺really✺ didn't want to talk to Joe Weirdo, so I just said “not particularly, no” and fortunately he went away.␤␤But what the actual f😵‍💫ck was this about? Is the AI sect recruiting random passers-by now?
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Anyway, I said “no, I'm French” (not exactly wanting to elaborate to Joe Random Weirdo that I'm also Canadian).␤␤Then he asks — and I kid you not — “are you interested in AI?”. 😲
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This is in a restaurant in a shopping mall. I was wearing motorcycle gear so I thought maybe he thought I was doing a ride through France or something, but I have NO idea why he would think I'm German. (I'm very blond, but not to the point that I seem out of place in France.)
Strange interaction just a minute ago. A guy I don't know walks up to me and asks (in English, with an 🇺🇸 accent): “Excuse me sir, are you German?”␤␤This is in 🇫🇷. He didn't ask if I speak English, he didn't ask if I was French, he came up right to me and asked if I'm German.
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* I mean “ℚ_p” above, not “ℤ_p”, of course.
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@JDHamkins For cross-references between social media plaforms: bsky.app/profile/gro-ts… pic.x.com/dB00PyIkSH
I'm sure there's already a sci-fi story out there where the AI alignment problem is solved and the first thing the benevolent superintelligent AI does is destroy all AIs including itself. x.com/AISafetyMemes/…
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The funniest thing about ChatGPT wrongly counting the ‘b’'s in “blueberry” is the AI fanboys who explain that the problem isn't reproducible, or goes away if you change the prompt slightly.␤␤I'm pretty sure PhD students get this right reproducibly, no matter how you word it.
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For those who missed the blueberry experiment: kieranhealy.org/blog/archives/…
So next time I run across a PhD student, I'll ask them to count the number of ‘b’'s in “blueberry” and report whether they're just as wrong as ChatGPT. x.com/NBCNews/status…
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… might be due to animosity toward the British, who, conversely, tend to forget that Ireland exists and no longer is theirs. Still, I'd be curious to ask the Brits who feel the UK isn't part of Europe to think about whether Ireland is (please draw Europe's boundaries!). •18/18
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… (despite many of the reasons ①–⑥ above applying equally well to Ireland). And it's maybe not an accident that Lord Castlereagh (whom I mentioned in tweet 12 above) was born and grew up in Ireland. Of course, part of the Irish pro-European sentiment … •17/18
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But there's another point that keeps getting forgotten whenever anyone discusses whether the UK is part of Europe, and that is Ireland. I hope I'm not wrong to believe that, unlike the Brits, the Irish very much feel part of Europe and of the European Union … •16/18
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Even that buffoon Boris said after Brexit that the UK is leaving the EU but “the UK isn't leaving Europe”. And I suspect Brits, despite their frequent denial, must be aware of the reasons I just laid out why the UK is (volens nolens) part of Europe. •15/18
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The war in Ukraine has forced all sorts of people to remember that Europe goes as far east as Kyiv, and, whether we like it or not, Moscow, but I think it may have also forced many to remember that London is also part of that same continent. ❦ •14/18
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And Ⓒ geopolitically, right now, the UK finds that it is inextricably linked to the common affairs of Europe, on all sorts of issues from the migrant crisis to how to react to the Trump presidency to, of course, the war in Ukraine. •13/18
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… I think a major event defining modern Europe and setting the stage for all later events is the Congress of Vienna of 1815, establishing the “Concert of Nations” of Europe, of which British FM Castlereagh was a major proponent, and in which the UK was a key great power. •12/18
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Ⓑ Historically, the UK has always been a major player in Europe's history. Even if we don't go back to the Anglo-French wars of the Middle Ages or the connections of the British royal family just about every other European country, … •11/18
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… large enough so you might consider it a country on its own (or part of an oxymoronic “continent” of “Oceania”), nor even like Iceland or Russia, kind of torn between continents. The only plausible answer to “what continent is the UK part of?” is “Europe”. •10/18
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Of course, the UK ✽is✽ part of Europe, in my opinion, for at least three important reasons. Ⓐ The first is a trivial geographical reason: Great Britain surely isn't in the Americas, Africa, Asia or Antarctica. And it isn't like Australia, … •9/18
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OK, that's just my summary, and I hope I didn't do the arguments great injustice. Note that he's not trying to argue that the UK ✽isn't✽ part of Europe, just explain why the Brits tend to think that it isn't (as polls show). And I think these are interesting points. •8/18
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⑥ Language: the fact that English has become the one global language (and the fact that it's called “English”, not “American”) makes the Brits feel that they are global players, but also has the effect that they consume very little culture from, say, France or Germany. ❦ •7/18
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This [in the video author's opinion — I'm still just summarizing here] explains why Brits view (e.g. EU) regulation with suspicion. ❧ ⑤ Monarchy: even if it's merely symbolic, the monarchy ties the country to its history [this is mostly a repeat of point ③, I think]. •6/18
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④ Legal framework: the UK (well, England) uses Common Law, “bottom-up”, mostly based on court case precedent, while the rest of Europe uses the Romano-Germanic system also known as Civil law, “top-down”, and mostly based on (a priori) codified written law. •5/18
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② Empire: the UK still feels a greater connection with its former colonies (Commonwealth nations) than to European countries. ❧ ③ No revolution: unlike other European countries, many British legal traditions and institutions go all the way to the Middle Ages. •4/18
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① Geography: obviously Great Britain is an island, and it's not just that this sets it apart physically, but it has allowed the UK to stay apart from the shifting boundaries of continental Europe, or to take sides in wars only as and when it sees fit. •3/18
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So, to summarize, the author of the video suggests six major reasons, none of which suffices alone (or is unique to the UK), but the conjunction of which explains why the Brits feel apart from the rest of Europe: … •2/18
This video tries to explain why the British think they're not part of Europe. Here's an attempt at a summary, with a few additional thoughts of mine. 🧵⤵️ •1/18 youtube.com/watch?v=d-skVy…
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… qui a lui-même engagé encore un autre tueur à gage, et au bout de 5 niveaux(!) de sous-traitance le 5e tueur a essayé de négocier auprès de la victime de simplement disparaître, et elle l'a juste dénoncé à la police. youtube.com/watch?v=ZETvtp…
Les entreprises aiment tellement tout sous-traiter que c'est parfois un peu miraculeux que la récursion termine. Ça me fait penser à cette histoire d'un type qui avait engagé un tueur à gage… qui a lui-même engagé un autre tueur à gage pour faire le boulot, …
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@laurentbercot (And part of that is to remember that I am the crowd no less than they are.)
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@laurentbercot I also have agoraphobia (well, “enochlophobia”). But the crowd is an emergent phenomenon, and, I agree, a potentially dangerous one. I don't see any contradiction between seeing the crowd as threatening and remembering that the individuals that constitute it are (typically) not.
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The ‘Atlas of Obscure Sorrows’ calls this “sonder”. And I think it can be a transformative experience to try to actually feel this as an emotion. youtube.com/watch?v=AkoML0…
Next time you're in a crowded place, take the time to contemplate the fact that every single person around you has a life, internal experience, social connections, story, memories and feelings, as rich and complex as your own. And for them you are just a face in a crowd.
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(Pour les lents à comprendre comme moi: en fait c'est la compagnie Audible GmbH qui est enregistrée auprès de ce tribunal.)
Une pub pour Audible dans le métro parisien (par ailleurs illustrée par une image IA merdique) porte la mention «enregistré […] au tribunal de Charlottenburg, Allemagne». Pdt un temps, j'ai cru qu'ils disaient enregistrer leurs audiobooks dans la salle d'audience du tribunal. 😅
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Et un peu plus tôt dans la saison, la A6 était totalement fermée dans le sens Paris→sud. Faire ça au même moment que le RER est totalement coupé, c'est vraiment une magnifique façon de dire «f🖕ck you» aux Parisiens qui ne sont pas partis en vacances.
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‣ coupure totale du RER B vers le sud tout l'été (interruption entre Massy-Palaiseau et la Croix de Berny du 15 juillet au 27 août),␤␤‣ nombreuses fermetures sur la A6 (en ce moment: liaisons A6a-A6b fermées, 1 voie fermée sur la A6a dans chaque sens, accès A6b Gentilly fermé).
Il est apparent par le nombre de travaux partout que la région parisienne subit le contrecoup des jeux olympiques de Paris 2024: chantiers qui auraient dû avoir lieu l'été dernier et qui ont été repoussés d'un an pour éviter de gêner les JO.␤␤Rien que pour le sud: …
Why the f🤨ck is Jeffrey Epstein shown reading a book on “multiple Dirichlet L-functions” in this (not super funny) ‘Tom the Dancing Bug’ comic? Is there a deep joke I missed? (Like: the first half of Dirichlet's name is “Lejeune”?) Or is it just random? boingboing.net/2025/08/06/tom…
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… une entrée existe depuis la voie publique ouverte à la circulation, mais il faut vraiment la connaître pour la trouver: le parc est situé à Magny-les-Hameaux, mais est accessible uniquement depuis une rue difficile à trouver à Voisins-le-Bretonneux. google.com/maps/@48.75076…
Un joli petit jardin qui est aussi une curiosité géographique: le parc de la Croix du Bois à Magny-les-Hameaux (Yvelines). openstreetmap.org/?mlat=48.75067… Ce qui est curieux, c'est qu'il s'insère dans la forêt domaniale de Port-Royal, et il a une entrée depuis la forêt; … pic.x.com/g2uIKDYD7S
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Concerning the Voynich manuscript: x.com/gro_tsen/statu…
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The video youtube.com/watch?v=qy72aU… will tell you more.␤␤(But, like the Voynich manuscript, I suspect there isn't much of to say except that some people have too much time on their hands to craft mysteries, and others enjoy them a little too much for their own sanity.)
Apparently the web site (blog?) ‘Forgotten Languages’ …languages-full.forgottenlanguages.org is a kind of equivalent of the Voynich manuscript in the era of the World Wide Web. By which I mean, nobody really knows what it's about, but there are many weird theories. …
RT @ngspiensfr: Je partage ce site, « abandonware-magazines », où on trouve des scans de plein de vieux magazines d'informatique et de jeux…
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TBH, I'm confused by the fact that the question seems to be suggesting one can turn a sphere inside out without self-intersection, which AFAICT is wrong — one can do it with immersions, but not with embeddings.
A mathematician is someone who, because they are trying to flip their grocery bag inside out due to the rain, starts wondering: “Does gusset-induced flexibility reduce critical bi-Lipschitz constant for sphere eversion?” 😁 mathoverflow.net/q/498768/17064 pic.x.com/rWcTBtRfGm
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[Source: Mathieu Sapin dans la BD “À l'intérieur”.]␤␤J'apprécie en tout cas qu'ils aient compris que les entiers naturels ne sont pas une ressource rare et qu'il n'est pas indispensable que tous les numéros pairs avant existent ds une rue pour avoir un 36. x.com/gro_tsen/statu…
Il paraît que la direction de la Police judiciaire de Paris, qui a déménagé en 2017 du fameux 36 quai des Orfèvres à la rue du Bastion (dans le 17e arrondt) a obtenu exprès de la mairie de Paris que la rue soit numérotée de façon à ce qu'elle conserve le numéro 36. pic.x.com/ZRyICS9chA
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@JacqBens J'avoue qu'une IA m'a aidé ici à trouver une formulation reflétant un certain niveau d'exaspération tout en restant poli. Ma rédaction spontanée était… moins civilisée. 😅
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@laurentbercot @ngspiensfr I am also pretty incapable of visualizing things in 3D. But as the standard saying goes, “in mathematics, you don't understand [or see] things, you just get used to them”.
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@laurentbercot But you are right to object: the partition of space into unit circles is impossible to visualize bc it is done by transfinite induction (and implicitly using the axiom of choice a lot). However, IIRC, there is a nice geometric one if we allow the radii to vary (but remain >0).
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@laurentbercot … And yes, we can partition space into lines, which is pretty trivial (just take all lines parallel to a given direction). And the same proof as for circles (so, far less trivial than for lines) will also work for unit squares, or unit equilateral triangles.
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@laurentbercot Well, to start with, mathematicians will partition the space in points, and that is trivial. 😆 (Note that I use the term “partition”, not “pave”, which is reserved for things like you more likely have in mind. “Partition” is more low-level, if you will.) …
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@ngspiensfr (Et bien sûr, même si les parcelles autour sont privées, le chemin entre elles peut quand même être public. La carte des limites de parcelles geoportail.gouv.fr/carte?c=6.6256… suggère que ton point est dans une parcelle, pas entre, mais je ne sais pas si c'est hyper fiable.)
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@ngspiensfr … que c'est une forêt privée, mais je ne sais pas à quelle point cette déduction est vraiment correcte, et en tout cas je ne sais pas comment en savoir plus (sauf chercher des indices sur le terrain comme des panneaux qui diraient «propriété privée défense d'entrer» 😅).
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@ngspiensfr Je ne suis pas sûr. La couche «forêts publiques» de Géoportail, geoportail.gouv.fr/carte?c=6.6256… montre que ton point n'est pas dans une forêt publique, alors que la couche «carte forestière» geoportail.gouv.fr/carte?c=6.6256… le montre bien comme étant en forêt, ce qui ✵suggère✵ …
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@ngspiensfr … mais elle doit être minimale et d'ailleurs difficile à faire valoir.) Et oui, c'est merdique.
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@ngspiensfr Note que “chemin de grande randonnée” est un label attribué par une association qui n'a rien de vraiment officiel, et qui ne préjuge rien du statut légal du chemin. Ça peut être une servitude sur un terrain privé. (Le propriétaire a alors une obligation d'entretien, je crois, …
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@laurentbercot To be 100% clear: to define a unit circle, you take a plane Π in space, a point O on that plane Π (which will be the circle's center), and the circle is the set {P∈Π : OP=1} of points P on Π such that the distance OP is exactly 1.
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@ngspiensfr @laurentbercot Ah, here's one way to prove it: reddit.com/r/mathriddles/…
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@ngspiensfr @laurentbercot IIRC, it is in fact not possible to partition space (ℝ³) into spheres of strictly positive (>0, not required to be constant) radius. But (also IIRC) this fact is not nearly as obvious as one might think.
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@laurentbercot A unit circle is a (plane) circle of radius 1. In other words, the intersection of a sphere of radius 1 with a plane that goes through the center of that sphere.␤␤The goal is to write space as the union of (necessarily uncountably many!) such circles, pairwise nonintersecting.
Les banques françaises, c'est 5 minutes pour ouvrir un nouveau compte, mais 3 mois pour le fermer. pic.x.com/1evQwOTOcj
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(Note that the question was edited after it was asked, so some of the MO answers are answers to slightly different questions, e.g., “circle” might refer to something that is topologically a circle but not necessarily a Euclidean circle as the question now stands.)
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The approved answer would also make a good ad for transfinite recursion: given the hint “use transfinite recursion on 𝔠 (the continuum)”, if you understand it, a seemingly very challenging question suddenly becomes quite easy. mathoverflow.net/a/28650/17064 pic.x.com/UtyaLxYqxp
This is a strong candidate for an “ask a interesting math exercise with the shortest question possible” challenge: can you write ℝ³ as the union of pairwise disjoint circles of radius 1? mathoverflow.net/q/28647/17064 pic.x.com/c9OYB3JAo7
RT @niccruzpatane: This is the greatest argument I’ve heard for why electric vehicles are better than gasoline-powered cars. amandeep.ca/tco…
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* I meant to find A⊆ℝ, of course, not A⊆ℝ³ (it's S that's a subset of ℝ³).␤␤I got an answer by James Hanson mathoverflow.net/a/498711/17064 (which I didn't check thoroughly yet), asserting that, under CH, one can indeed find A⊆ℝ such that S is connected.
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This follows an earlier question (not by me): is the set of points of ℝ³ with exactly one coordinate rational (i.e. the case A=ℚ in the previous question) connected? The answer is negative. mathoverflow.net/q/498647/17064
I asked on MathOverflow whether it is possible to find A⊆ℝ³ such that the set S of points of ℝ³ with exactly one coordinate in A is connected. (Note: it is quite possible that this is a stupid question.) mathoverflow.net/q/498699/17064
RT @ngspiensfr: Cookie-based async system calls: what do you think of it? Unix has the aio API to do reads and writes asynchronously; on Li…
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@Vicnent C'est vraiment différent: s'il y a 4 stops, tout le monde est à l'arrêt, donc proba d'accident grave très faible, et dans le doute tu piles. Là on parle de voies rapides où tout le monde va vite et tu ne peux pas t'arrêter dans le doute. Ce serait bien d'avoir une règle claire!
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Clairement Ⓐ&Ⓑ ont priorité sur Ⓓ. Comme Ⓐ n'est pas en conflit avec Ⓑ&Ⓒ, pas de question là-dessus. La question qui se pose surtout, c'est entre Ⓑ et Ⓒ: qui a priorité, entre qui change de file pour sortir et qui reste sur sa file mais a un cédez le passage? •3/3
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Je considère 4 types de véhicules: Ⓐcirculent à gauche (voie rapide) et y restent, Ⓑviennent de la gauche (voie rapide) et sortent, Ⓒcirculent sur la voie d'entrecroisement (droite), et Ⓓviennent de la droite (entrecroisement) et s'insèrent. Quel ordre de priorité?… •2/3
Question sur le code de la route français: considérons une voie d'entrecroisement (i.e., à la fois entrée et sortie sur une voie rapide), qui vient jouxter une voie rapide par la droite. Il y a un panneau “cédez le passage” sur la voie d'entrecroisement. … •1/3
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Note: Marie Curie isn't just the only person in the photo with more than one Nobel prize: in 1927 she was the only one in the world, and would remain so for 35 more years. Only 5 ppl have ever been awarded multiple Nobels, and only 2 in different fields (M.C. and Linus Pauling).
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… It's because she is the only person in the photo with TWO Nobel prizes, surrounded with all those dimwits who only had one (or none). 😄
This famous photo of the Fifth Solvay Conference in physics (1927) has been called the highest concentration of intelligence in a single photo, with circa 17 Nobel prizes together (see alt text for names). But do you see why Marie Curie must have felt lonely in that group? … pic.x.com/oyV9PriaVR
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@drmtgr To be clear: the way the basic transformer models are set up (with “attention”), they do have an arrow of time. But this can, of course, be reversed because everything is symmetrical. What I am asking is, whether someone tried doing this to see how it behaves.
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@miaoubete You are given the end of a sentence or text and you try to generate a plausible beginning. Or you are given an answer and you try to generate a plausible question for it.
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@odtorson 🤫 We don't want to risk the Universe being replaced by something even more bizarre and inexplicable.
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(This very shitty shower thought is brought to you by the passing idea: “is there a way to recover the most likely prompt that caused an AI to generate some text? — oh, maybe we can train an AI to do exactly that!”)
Semi-serious question: has anyone tried running LLMs backwards? That is, instead of training them to do NEXT word prediction, you train them to do PREVIOUS word prediction. And to question answers instead of answering questions. How does this turn out?
I dreamt that I was (accidentally) invited to Jeff Bezos's birthday party. (Which was mostly just a display of very expensive sports cars. Also, I was the only one who had come by train.)␤␤What a horrible dream.
Quelques réflexions sur le porno comme canari dans la mine des libertés fondamentales, en l'espèce de la liberté d'expression en ligne: comment la France et le Royaume-Uni utilisent le prétexte de protéger les mineurs pour censurer Internet: madore.org/~david/weblog/…
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How image generating AIs and diffusion models, work mathematically: youtube.com/watch?v=iv-5mZ… (not everything was perfectly explained, I thought, but I still learned a lot).␤␤By the same guy who did these very interesting videos on discovering Kepler's laws: x.com/gro_tsen/statu…
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On the history of German bureaucracy, from the HRE through Prussia and Nazism to the modern days (a but hard to summarize, but very interesting): p1: youtube.com/watch?v=oRBBoZ… / p2: youtube.com/watch?v=RPri_e…␤␤(I watched this one a while ago but I don't think I shared so far.)
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@laurentbercot That one definitely goes into the “reasons to have a bird” category. Parrots are awesome. If I had one I would definitely teach it some orgasm sounds it can repeat when there are visitors around.
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@laurentbercot Your thinking is confused. This is just a reason not to set an alarm clock.
Le même jardin porte deux pancartes: une qui annonce qu'il est ouvert tard le soir jusqu'au 7 septembre, et une autre qui annonce qu'en fait il est fermé pour travaux jusqu'au 1er septembre. 😕 pic.x.com/TvGCvwqDsx
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So, I just sent this email to the UPenn librarians. We'll see if something comes out of it! pic.x.com/Fa6Jbv1EpF
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@laurentbercot Yeah, the sheet music deserves praise of its own!
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How self-censorship, and external censorship, of taboo words, e.g., on social media, makes language evolve in creative ways: youtube.com/watch?v=O0SjTK…
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A fun and jazzy interpretation of Pachelbel's Canon in D on piano (and… metal ruler?), in which the performer seems to be enjoying herself tremendously, and the audience as well: youtube.com/watch?v=lpc1lE…
RT @JdponTransfem: On assiste tout simplement à la mort d'internet. Ce qui se joue c'est un truc voulu longtemps par les institutions occid… x.com/GBPolitcs/stat…
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“He hosted the press conferences […] in the newly renovated ballroom at Turnberry, boasting of the opulent new ceiling and brand new windows at the same time as discussing famine in Gaza.”
“It is exceptionally unusual for a US president to so nakedly use his office to promote his own commercial interests but it is something Donald Trump clearly revels in doing.” 😑 bbc.com/news/articles/…
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The story of emoji and who decides what gets to be an emoji or not: youtube.com/watch?v=E4DaZa…
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On the economics of YouTube channels and why many independent channels are being bought by private equity: youtube.com/watch?v=hJ-rRX…
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A deep sociohistorical dive into the relations between men and women in China: youtube.com/watch?v=5-QpCN…
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A trans guy explain why being stealth doesn't only have upsides: youtube.com/watch?v=R3Y54C…
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The story behind Brussel's special place in European institutions: youtube.com/watch?v=cD9_AK…
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Explaining that whether several notes sound harmonious or dissonant depends mostly on their overtones (which may or may not be simple integer harmonics): youtube.com/watch?v=tCsl6Z…
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On the Vatican's finances, and how and why the Holy See ends up being tied to shady real estate deals: youtube.com/watch?v=9027XC…
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On Dick Cheney, and how he came to be so influent as vice-president: youtube.com/watch?v=GJA_Sh…
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On the life and works of Marie Curie (this is the first part, with another one to com): youtube.com/watch?v=gR9OPU…
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On the geometry of the space of colors [in French]: youtube.com/watch?v=NuDhD6…
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Does the Chinese language have words? Not an obvious question, as this linguist explains: youtube.com/watch?v=kCSe3d…
A few YouTube videos I watched recently and found interesting enough to share (note that my tastes are pretty eclectic): 🧵⤵️
The idea that the ergodicity of a rotation by an irrational number of turns was proved by Nicolas Oresme in his 1360 ‘De commensurabilitate vel incommensurabilitate motuum celi’ is a bit far-fetched, but that would be super cool to cite as a reference: mathoverflow.net/a/269895/17064
Petite réflexion (pas trop interminable, pour une fois) sur mon blog sur les choses qui m'aident à me sentir chez moi, et pourquoi je n'aime pas voyager: madore.org/~david/weblog/…
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@GenevieveMadore C'est déjà fait (email au greffe du tribunal + envoi papier par recommandé). Mais comme en principe je m'étais engagé à utiliser ce site, je préférerais qu'il remarche, pour être sûr. x.com/gro_tsen/statu…
Du coup, je dois demander: si le greffe du tribunal administratif me dit que mes observations doivent être «produites dans un délai de 1 mois» par un courrier daté du 30 juin 2025, ça veut dire que j'ai jusqu'au 30 juillet 2025… inclus ou exclu? x.com/gro_tsen/statu…
RT @gracecamille_: are there other pics like this? I am compiling pic.x.com/kQT0FnvhaQ
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Bon ben ils auront les pièces par courrier papier + email, avec un mot explicatif adressé au greffier pour expliquer que c'est pas ma faute, capture d'écran à l'appui.␤␤Mais ça fait un facteur de stress en plus dont je me serais bien passé.
Bon, je fais un recours au tribunal administratif une fois dans ma vie, je me suis engagé au moment de l'enregistrement de la requête à utiliser le site “Télérecours Citoyens” pour déposer les pièces, et le jour d'une deadline, France Connect est en rade. 😭 pic.x.com/nn3vUz2JJt
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More commentary from another historian: x.com/BretDevereaux/…
One of those beautiful moments where Grok's made-up bullshit gets caught and pointed out by the very historian it was citing. 🤩 pic.x.com/1Qc63NmDy4 x.com/WalterScheidel…
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@JPBillingsgate His response was even less subtle. pic.x.com/NUkZcDsDqq
Social media be like: pic.x.com/3jH42tZx3U x.com/RasmusJarlov/s…
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PS: I'm told that there is, in fact, a biopic (of sorts) of Sir Arthur Stanley Eddington: it's called ‘Einstein and Eddington’ (2008), and apparently it's not bad. imdb.com/title/tt099503… x.com/EvarixGaulois/…
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@espie_openbsd Ce n'est pas que la touche Compose, d'ailleurs: si on fait control-shift-u suivi d'un numéro (pour saisir directement un caractère par numéro Unicode, ce que je fais assez souvent), la même chose se produit.␤␤Je n'ai jamais vu ce problème ailleurs que sur Twitter.
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@espie_openbsd Oui, je l'utilise aussi, et, oui, j'ai remarqué la même chose que toi. Et j'utilise le même palliatif.␤␤(Bon, en fait, je rédige de plus en plus sur Bluesky en premier, et je copie-colle sur Twitter ensuite, alors qu'avant je faisais le contraire.)
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@EvarixGaulois Ah! Maybe I had heard that one being mentioned somewhere recently, and because of that I thought the new unrelated movie was in fact about Sir Eddington. Thanks.
I saw posters for a movie called ‘Eddington’ and was sorely disappointed to learn that it's not a biopic of Sir Arthur Stanley Eddington (I would watch that!).
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@BallouxFrancois Just don't abandon it on the side of the road on your way on vacation.
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@LYMFHSR 41 donc encore +5(?) parce que Charlemagne a des ancêtres documentés.
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@LYMFHSR De façon moins personnelle, quelle est la relation ancêtre-à-descendant-direct la plus longue (en années ou en générations) qu'on puisse établir de façon fiable? Je donne 41 générations entre Charlemagne et le comte de Paris ici: madore.org/~david/weblog/… — mais il y a p-ê mieux.
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@LYMFHSR @BhTyphon Obligatory Existential Comics: existentialcomics.com/comic/281
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So there's incontrovertible evidence that this image dates ✺at the latest✺ to the summer of 2001: archive.org/details/altern… — and probably fall of 2000: x.com/JeanDellass/st… (but this is still probably a reprint of something published earlier).
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@JeanDellass Quelqu'un m'a suggéré “Alternative Press Review” sur l'autre réseau aussi, mais je suppose que le nom suggère que ce sont des reprints de choses déjà parues ailleurs. Mais au moins ça donne un majorant sur la date de publication.
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If your name is “Thompson”, please don't ever discover another interesting simple group, thanks in advance.
“Thompson's group” in mathematics can refer to either the finite simple group with 90 745 943 887 872 000 elements discovered by John G. Thompson, or to an infinite simple group discovered by Richard Thompson. This is NOT AT ALL CONFUSING. #ContextClub
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@evolvepolitics Every. Single. Time. x.com/gro_tsen/statu…
Side question for historians of the Internet: what is the exact source, date and original context of this comic?␤␤I know the author is John Jonik en.wikipedia.org/wiki/John_Jonik — it was probably published in the NYT or New Yorker in the early 2000's, but when, exactly, and what about? x.com/gro_tsen/statu…
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Cette loi aurait dû faire réagir au moins autant que la loi Duplomb, mais les gens sont manipulables: on leur dit que c'est pour protéger les enfants, ils y croient; on leur dit qu'Internet c'est technique et ne les concerne pas, ils y croient aussi. x.com/gro_tsen/statu…
Et les Français ne devraient pas rigoler: la France a voté une loi complètement conne (loi legifrance.gouv.fr/jorf/id/JORFTE… «visant à sécuriser et à réguler l'espace numérique» 🙄) aussi sous le prétexte bidon de protéger les jeunes contre le porno, qui permet aussi ce genre de censure. x.com/gro_tsen/statu…
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Meanwhile, the top comments on this site are… the deep analysis you would expect from the comments on this site. 😓 pic.x.com/jIYXhKoa6M
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As usual, it's either “we need this to protect you against the dangerous terrorists” or “will someone please think of the children?”.␤␤(This cartoon is at least 20 years old, by the way. Some things just don't change. People fall for it every time.) pic.x.com/1IzLuRybVA
The United Kingdom — the “land of the Magna Carta” — is poised to censor or block access to Wikipedia because WP isn't safe(?) for minors(???).␤␤Meanwhile, despite all the fake news and AI slop, Wikipedia remains one of the most effective tools against disinformation.␤␤😭 x.com/evolvepolitics…
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@archimate @dylanmallman For lack of space, I used “ideas” in wide sense: works of art, programs, inventions, count as “ideas” in the sense of the previous tweet. There shouldn't be ownership of any such things (bc their usage is not exclusive), merely “paternity”.
RT @gro_tsen: @dylanmallman I've said it before and will say it again: the very term “intellectual property” is a PR move to try to attach… x.com/gro_tsen/statu…
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@dylanmallman I've said it before and will say it again: the very term “intellectual property” is a PR move to try to attach the property rights on ideas. It makes no sense.␤␤What makes sense is “intellectual paternity”: your ideas are your creations, not your property. x.com/gro_tsen/statu…
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… il passe en mode «je ne sais pas», bref, il semble juste montrer le dernier panneau qu'il a vu (et parfois mal vu), c'est tout. Heureusement, ça ne bippait pas quand je dépassais la vitesse qu'il pensait avoir lue, sinon je serais devenu fou! •12/12
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Et ⓑle truc censé lire les panneaux de limitation de vitesse pour afficher la limite est COMPLÈTEMENT NUL. Mais nul de chez nul. Il ne comprend pas les panonceaux, il ne semble pas retenir la valeur par défaut dans une agglo, s'il y a un panneau «fin de limitation» … •11/12
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… mais la voiture ne l'a pas reconnu, ou affichait un message d'erreur sibyllin. Or naviguer avec le téléphone posé sur le siège passager (pq pas de support où le mettre), c'est très malcommode, même avec la voix activée. D'ailleurs, cette voiture n'a pas de GPS intégré? •10/12
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Deux griefs cependant. ⓐJe n'ai pas réussi à activer Android Auto (le truc qui permet d'avoir la navigation du téléphone sur l'écran de la voiture). Je ne sais pas pourquoi. Mon téléphone prétend qu'il l'a, et qu'il détecte automatiquement la connexion, … •9/12
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… qui est plus proche du frein moteur d'une moto (→ si on lâche l'accélérateur, ça ralentit fortement), je trouve ça vraiment plus plaisant à conduire (et plus sécurisant!) que ces voitures qui continuent à vitesse constante quand on lâche les pédales. •8/12
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… plus une option d'assurance à 4.99€ (que je n'étais pas obligé de prendre). La voiture était propre, plutôt en bon état (juste qqs dommages esthétiques sans importance). Elle est plutôt plaisante à conduire. J'apprécie le mode ‘B’ (=plus de freinage régéneratif), … •7/12
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Mais c'est théorique, et je n'ai pas eu de pb.) La location m'a coûté 45.07€: ça se décompose en 0.99€ de tarif de base, plus un tarif horaire, pour lequel j'ai pris un forfait 6h qui était en promo à 21.99€, plus un tarif kilométrique de 57km × 0.30€/km = 17.10€, … •6/12
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L'app aime bien désactiver le moteur de la voiture dès qu'on le coupe pour plus que qqs instants. Si la couverture réseau est aléatoire, elle pourrait bien réussir à le faire et ensuite ne plus réussir à le réactiver. C'est un poil stressant. Surtout si on va en forêt. •5/12
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Pour ce qui est de l'app Android Free2Move, je dois dire qu'elle est plutôt bien faite. Elle est assez intuitive à utiliser, la location va vite. (J'ai qd même un doute qui m'angoisse un peu: il se passe quoi si on emmène la voiture à un endroit où le téléphone capte mal? •4/12
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… quant au poussinet, ben il est parti à la montagne avec une de ses voitures, et disons que je ne me sens pas à l'aise à sortir l'autre de notre parking. Laquelle est d'ailleurs une thermique, alors autant louer une électrique.) •3/12
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(D'abord, si on se demande pourquoi je loue une voiture alors que j'ai deux motos et que le poussinet a deux voitures… le problème de la moto, c'est qu'il faut porter un équipement dont on ne sait pas quoi faire ensuite quand on va qqpart pour se balader, … •2/12
Alors, j'ai loué une voiture Peugeot e-308 (électrique, donc) avec Share Now pour faire un aller-retour Paris↔︎Draveil (pour me balader dans la forêt de Sénart). Quelques petites remarques si ça intéresse qqn. 🧵⤵️ •1/12 x.com/gro_tsen/statu…
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@laurentbercot @Vicnent L'assistance juridique, que je sache, c'est pour les litiges de droit civil, pas pour les litiges administratifs (enfin, celle de mon assureur). Et je n'ai juste pas les moyens de payer un avocat.
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@laurentbercot @Vicnent Il pourrait mal se passer que je perde, ce qui est hautement probable, mais je ne perds rien parce que je n'ai pas d'avocat à payer et que le recours au juge administratif est gratuit, c'est l'intérêt par rapport au civil.
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C'est bien gentil de dire que les Parisiens ne devraient pas avoir de voiture individuelle, mais pour que ça puisse marcher, encore faut-il que ce soit possible de louer une voiture ponctuellement, simplement et sans s'arracher les cheveux. •4/4
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… tué son propre service et repris celui de Share Now sous sa propre marque). Ubeeqo a l'air mort: il prétend être repris par Europcar On Demand, sauf que ceux-ci ne font pas Paris donc je ne comprends pas. COMMENT TROUVER UNE LISTE FIABLE ET À JOUR, BORDEL‽ •3/4
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Avant il y avait Autolib. Qui a été tué. Puis il y a eu (au moins) Moov'in, Free2Move, Car2Go, Ubeeqo, Communauto. Moov'in a disparu. Car2Go s'est renommé en Share Now, et a été racheté par Free2Move et fusionné avec (mais en fait je crois que Free2Move a … •2/4
Les services de location de voiture à la demande à Paris, ils n'arrêtent pas de changer de nom, de faire faillite ou de se faire racheter, tellement vite qu'à chaque fois que je décide d'essayer de m'en servir, tout a changé et il faut que je redécouvre ce qui existe. •1/4
RT @ngspiensfr: La désinformation par paywall, un concept intéressant. J'ai envie de répondre : la partie de la publication qui n'est pas d… x.com/legeniehumain/…
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Links re SCotUS case and the quote by Anatole France: x.com/gro_tsen/statu…
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Links re Trump executive order: reuters.com/world/us/trump… ❧ npr.org/2025/07/24/nx-… ❧ washingtonpost.com/health/2025/07… ❧ theguardian.com/us-news/2025/j… ❦
“The law, in its majestic equality, forbids the rich and poor alike to sleep under bridges, to beg in the streets, and to steal bread.” pic.x.com/0gBG2FVAUw x.com/gro_tsen/statu…
Moi (non juriste) en train de rédiger des observations en réponse au mémoire en défense soumis par mon employeur dans un recours que j'ai déposé contre lui devant le tribunal administratif de Versailles (concernant l'alimentation de mon compte épargne-temps). pic.x.com/7na7oFyzYe
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* il a refusé (pas «on lui a refusé»)
Ce type a failli être prince consort du Royaume-Uni, on lui a refusé de devenir roi de Grèce, et finalement il est devenu le premier roi des Belges. fr.wikipedia.org/wiki/L%C3%A9op…
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Also, he complained that he couldn't decide whether to sit with the table's leg to his left or his right, so there was the occasion of a lifetime to make a joke about spontaneous symmetry breaking, I tried, it came out wrong, nobody laughed, and now I'm forever mortified.
So, I met François Englert¹ at a mutual friend's place tonight, and he said that he had found J. Robert Oppenheimer insufferable. #CelebrityNews␤␤1. Of Brout-Englert-Higgs fame.
RT @gro_tsen: @IanSolliec @laurentbercot … but in theory, not only does special relativity not prevent you from visiting the Andromeda gala…
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@IanSolliec @laurentbercot … but in theory, not only does special relativity not prevent you from visiting the Andromeda galaxy in your lifetime, it ✸allows✸ it — whereas Newtonian mechanics (or even a much larger speed of light!) would forbid it.
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@IanSolliec @laurentbercot … because constant acceleration in special relativity gets you exponentially far w.r.t. proper time, so you could even reach other galaxies that way). Of course, this does require ludicrous amounts of energy, and the amount of time measured by observers at rest is huge, …
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@IanSolliec @laurentbercot “Well, akshually…”␤␤Even in a nonrelativistic universe you can't reach a star more than a few thousand light-years away because of the constraint of not accelerating too much (that would crush a human body). Whereas with relativity you can go very far with 1g acceleration …
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En bon compris 🇪🇺, je pense que cette gare devrait avoir 24 noms officiels, plus encore un en latin (“Brucsella meridionalis”?) qui serait utilisé quand il ne faut fâcher personne. In varietate concordia, tout ça tout ça.
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Wikipédia l'appelle “Brussels-South” en anglais, “Bruxelles Sud” en italien, etc. en pleind de langues. En allemand, c'est plus délicat, le titre est “Bahnhof Bruxelles-Midi/Brussel-Zuid” mais la première phrase commence “Der Bahnhof Brüssel Süd”.
Observation: sur les Eurostars ex-Thalys, lors des annonces, le personnel appelle la gare de Bruxelles-Midi “Brussel-Zuit” en néerlandais/flamand, mais “Bruxelles-Midi” en (français, bien sûr, mais aussi) allemand et anglais. Pas “Brüssel Süd” et “Brussels-South”.
RT @littmath: One worry I have is that AI tools will develop their ability to produce hard-to-check, convincing mathematical prose more rap…
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@laurentbercot (I also very much mind being trapped in a universe limited by the Church-Turing thesis, but that's another matter.)
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@laurentbercot I don't mind inhabiting the human body, I mind being trapped into it. 🫤
Please send help! I think I'm trapped in a human body and I don't know how to escape it.
I asked a question on MathOverflow about the consistency strength and arithmetical strength of the historical ‘Principia Mathematica’ system by Russell & Whitehead. mathoverflow.net/q/498078/17064␤␤(I'm amazed that I couldn't find the answer by simply googling. Maybe I googled wrong.)
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@titedino78 Peut-être bien. Je viens de tester sans ce renforcement (à la suite de ma conversation précédente), et il reconnaît m'avoir pipoté et ne pas identifier de chamois sur l'image. (Mais bon, ça peut aussi ne pas être reproductible.) pic.x.com/NWvazuDPBD
RT @whippletom: This is the tale of a little frog who could. That frog's name was Rosie the Ribeter. And she could jump over 2 metres. And…
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@alexis_gatier On n'est généralement pas décrédibilisé pour avoir commis des erreurs, en maths, ni pour ne pas les avoir détectées: ça arrive à tout le monde, même aux meilleurs. Évidemment, si ça se sait qu'il a refusé de relire les lemmes, c'est différent.
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@qlala1 This is why I wrote “I'm told that there is…” and not “there is”. In my case this was false, but in the case that I was reproducing it was entirely correct and sincere (the bf had actually been told that there was a chamois on the image and was really searching for it).
All I want out of life is more than my fair share.
Pour ce que ça vaut, je rappelle l'existence de la webapplication “Carto Tchoo” qui permet de visualiser la position en temps réel des trains en France. carto.tchoo.net/map/48.8623,2.…
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Left: the image I used (found by googling “chemin montagne jura”). Right: the one in which ChatGPT “highlighted” the chamois for me.␤␤Note how other things in the image have changed (like the textures, the path in the background, etc.). pic.x.com/6kwA0tGb58
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Link to ChatGPT conversation: chatgpt.com/share/687cd53a…␤␤Thanks to @Conscrit_Neuneu for pointing out such an example to me (he found it accidentally; this is an independent reproduction, on first try, with a different image, so the technique seems to be fairly robust).
A beautifully striking example of how AIs can hallucinate anything:␤␤I ask ChatGPT for help in finding the chamois in the picture (there is none), so it hallucinates one, helpfully proposes to highlight it, and… it just adds a chamois to the image. 🤣 pic.x.com/gpkMUpDIsw
“Vibe coding” AI tool (🤦) goes rogue, deletes entire database despite being explicitly told to freeze, and pulls out the “I panicked” excuse. 😂 x.com/jasonlk/status…
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Aussi les limites des forêts publiques montrées sur une carte: geoportail.gouv.fr/carte?c=2.3489… (merci à @conazole pour le signalement) x.com/gro_tsen/statu…
Je viens seulement de remarquer que Géoportail avait une info que je cherchais depuis longtemps: la carte des forêts de France montrant par un code de couleur les types de formations végétales (essences dominantes). geoportail.gouv.fr/carte?c=2.7002…
Je suis tombé sur ce jeu de données #OpenData avec la liste et les limites géographiques des forêts publiques en France métropolitaine, alors je partage: public.opendatasoft.com/explore/datase…
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@fredericln Le précédent directeur de l'ENS, physicien, s'appelle Marc Mézard. Mais je ne crois pas que ce soit la même famille qu'Ariane, c'est juste un nom courant.
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@SayahHajji On trouve plein de beaux garçons à l'ENS (ou en tout cas on en trouvait plein pendant que je hantais les lieux). Et pas seulement si on aime le look “premier de la classe”.
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Du coup, je me suis dit, il y a forcément un vrai matheux compétent qui a aidé la réalisatrice. Et de fait, j'ai regardé au générique, c'est Ariane Mézard, qui était au département de maths de l'ENS en même temps que moi, qui l'a conseillée. Donc merci à elle! •16/16
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Ce qui est sûr, c'est que les maths présentées dans le film, et même la façon des matheux de travailler ensemble, est assez crédible. (Bon, les tableaux noirs partout c'est exagéré, et ils sont trop bien organisés, mais l'idée générale est juste.) C'est super rare! •15/16
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(Bon, je suis d'accord avec une collègue que j'aurais plutôt vu — ou préféré voir — l'héroïne finir en couple avec sa colloc, ce qui n'aurait pas demandé grand changement au scénario sur le reste… mais ce n'est pas d'ordre mathématique, là.) •14/16
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Mais sinon, à part ce début que je trouve assez catastrophique, et le personnage du directeur de thèse que je ne trouve pas crédible du tout, le reste m'a bien plu. L'héroïne, elle, est crédible et attachante, et le cothésard à peu près aussi. •13/16
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(Une forme plus crédible de connarditude, par exemple, ce serait de voler les résultats du doctorant. Mais dans le film, justement, le directeur fait pression pour obtenir l'accord de l'héroïne pour mettre son nom sur un papier. Donc il ne se comporte pas comme ça.) •12/16
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Bon, le directeur de thèse est présenté comme un connard, et des directeurs de thèse qui sont des connards j'en ai vu (pas les miens! heureusement). Mais cette forme particulière de connarditude, franchement, je n'ai pas croisé. •11/16
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En tout cas, on ne dit pas à qqn qui a bossé 3 ans sur une thèse, «ah ben il y a une erreur, il faut repartir à zéro sur un sujet différent». On aura des résultats plus faibles, ou partiels, ou conditionnels, ou on travaillera pour y arriver autrement. Au moins on essaie. •10/16
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Et aussi, même si un résultat exposé dans un séminaire s'avère contenir une erreur, et qu'on s'en rend compte en live (ce qui est rare, mais ça arrive), on va dire quelque chose comme «on en discute ensemble après». Et c'est rarement totalement irrécupérable. •9/16
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D'abord, quand un matheux croit que quelque chose est complètement faux, il va dire «je ne comprends pas comment vous pouvez obtenir truc à partir de machin», pas «c'est complètement faux». (Parce que de fait, souvent ça ne l'est pas, on a vraiment mal compris.) •8/16
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Dans la scène du séminaire, les questions posées à l'héroïne sont parfaitement crédibles. Et puis vient la réaction complètement lunaire du directeur de thèse, «ça invalide tout votre raisonnement». Mais on ne dit jamais ça entre matheux! Surtout pas en public! •7/16
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Alors voilà, je trouve certains bouts de ce film hyper bien vus et complètement conformes à mon expérience du monde mathématique, et d'autres complètement invraisemblables. Parfois dans la même scène. C'est perturbant. •6/16
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J'ai aussi assisté à des séminaires où une erreur a été trouvée dans un résultat important en train d'être présenté (celui qui trouvait l'erreur était presque toujours Ofer Gabber, d'ailleurs, et plus d'une fois il l'a réparée en même temps qu'il la trouvait). •5/16
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Ah, et puis en gros un mois avant ma soutenance de thèse, mon directeur de thèse (le deuxième, donc) a trouvé une erreur assez grave dans un lemme clé d'un de mes résultats. (C'était réparable. J'ai dû tirer un corrigendum à part de mon manuscrit, qui était déjà imprimé.) •4/16
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Aussi, je me suis fait congédier par un premier directeur de thèse (qui a d'ailleurs eu des élèves bcp plus brillants que moi avant et après, dont 2 médailles Fields). Ça m'évoque des choses! (Mais bon, dans mon cas c'est parce que je foutais rien.) •3/16 madore.org/~david/weblog/…
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Je suis passé par l'ENS en maths, j'y ai enseigné, et par ailleurs j'habite dans le 13e, c'est dire si je connais les lieux. Il y a plein de scènes que je peux situer très exactement (dont, à l'ENS, la salle W, et le couloir de mon ancien bureau). •2/16
J'ai vu “Le Théorème de Marguerite”, et j'ai rarement été aussi partagé sur un film. Je n'ai pas (mais alors vraiment pas du tout) aimé les premières ~25min, et j'ai bien aimé en gros toute la suite. •1/16 imdb.com/title/tt266995…
RT @zoomerbread: @chachamyeon remember when people were laughing at north korea's "approved haircuts" pic.x.com/It8RlnGRWd
Energica semblait être la seule marque faisant des motos électriques sérieuses (avec une autonomie décente et acceptant la charge en courant continu). J'espère qu'un repreneur va continuer la série (même si, pour l'instant, elles sont complètement hors de prix). x.com/LeRepaire/stat…
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Bon, si on en croit cette carte postale trouvée sur eBay par un mutu sur Bluesky, ce serait le «kiosque du domaine de Millemont»: ebay.fr/itm/1855120310… pic.x.com/PUO52Mv6CC
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Tout petit élément à l'enquête: le bâtiment figure sur la carte de 1950 que Géoportail met en ligne: geoportail.gouv.fr/carte?c=1.7141… (en haut à gauche du ‘1’ de “184” à droite de “Butte du Tertre”). Donc ça donne une idée de date, mais ça ne nous dit quand même pas ce que c'est.
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Si quelqu'un veut enquêter (ou même simplement expliquer comment on ferait pour enquêter sur une chose pareille), ou émettre des conjectures, feel free.␤␤(L'endroit est un peu chiant d'accès. C'est peut-être une forêt privée, d'ailleurs, ce n'est pas clair sur les cartes.)
Il y a 3 mois, @Conscrit_Neuneu et moi sommes tombés sur cette étrange bâtisse en ruine au milieu d'une forêt. (Ici openstreetmap.org/?mlat=48.80888… dans la forêt des Quatre Piliers à Millemont, Yvelines — geoportail.gouv.fr/carte?c=1.7141… chez Géoportail.) Qu'est-ce donc que ce truc? pic.x.com/PeFxu6jmOR
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@laurentbercot (Le problème avec la compta publique, c'est que même si les maths sont triviales, juste des additions et des soustractions, les définitions sont souvent tellement épineuses que tu peux faire avaler n'importe quoi à n'importe qui en jouant dessus.)
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@laurentbercot … Je n'ai absolument aucun doute que plein de gens se sont arrangés pour que l'État leur verse une jolie petite rente sous forme de subsides, mais les chiffres que j'ai vu passer me semblent très suspects.
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@laurentbercot … mais si on va critiquer ça alors il ne faut pas critiquer le principe que les entreprises publiques cherchent à équilibrer leurs comptes (y compris pour remplir une mission de service public). Ceci étant, je n'ai pas fouillé. …
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@laurentbercot Pour ce qui est du montant des aides aux entreprises, il faut vraiment voir ce qui est dans le périmètre. J'ai cru voir passer des chiffres qui incluent le montant des aides aux entreprises publiques, ce qui est certes légitime à compter, …
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@laurentbercot … et au sens des critères de Maastricht c'est de toute façon inclus dans le périmètre du déficit public. Donc c'est une séparation complètement artificielle, mais qui marche très bien pour écarter en gros la moitié du budget de toute possibilité de discussion.
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@laurentbercot … alors que ce sont les mêmes députés qui votent les lois de financement de la Sécurité Sociale, ce sont quasiment les mêmes contribuables qui les paient, c'est effectivement un impôt (sur le travail), qui du coup limite l'acceptabilité d'autres impôts, …
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@laurentbercot Ce qui est surtout complètement dingue, c'est que cette spécificité comptable du système de retraites (héritée du moment où il était vraiment indépendant de l'État) qui le place complètement à part du budget de l'État le découple ipso facto du débat sur les comptes publics, …
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@laurentbercot Voici pour les ordres de grandeur (je n'ai pas vérifié le détail des chiffres, mais les o.d.g. sont cohérents avec diverses sources): x.com/VianneyMone/st…
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@AlcofribNasier Les fonctionnaires ne sont pas les seuls à subir les coupes dans les services publics ou la baisse de qualité consécutive à la baisse d'attractivité des métiers. Eux votent mais sont peu nombreux. Les autres qui le subissent ne votent pas (assez).
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… Et l'explication, c'est juste que vieux votent. À chaque élection. Même quand ils n'aiment pas les candidats. Alors que les jeunes non. Donc désindexer les retraites de l'inflation, même temporairement, c'est un tabou, mais pour le point d'indice des fonctionnaires, pas de pb.
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… LE truc que personne ne montre du doigt, ni à gauche, ni au centre, ni à l'extrême-droite, c'est la retraite des boomers (commodément séparée du budget général de l'État par la fiction comptable faisant des «cotisations sociales» autre chose qu'un impôt sur le travail). …
Je dirais plutôt:␤␤⁃ gauche: «c'est la faute des cadeaux aux entreprises et aux riches»,␤␤⁃ libéraux: «c'est la faute des assistés, des aides en tout genre»,␤␤⁃ extrême-droite: «c'est la faute des immigrés qui viennent vivre aux crochets de la France»,␤␤mais bizarrement … x.com/ordrespontane/…
RT @TheOnion: White House Evacuated After Trans Alarm Goes Off␤theonion.com/white-house-ev…
The only winner of the war of 1812 was Tchaikovsky.
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I posted an answer to my own question by describing what pre- and pseudotopological spaces tell us about quotients of topological spaces (and vice versa) and providing some hopefully illuminating examples: mathoverflow.net/a/497830/17064
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This is probably a better/simpler example of a hereditarily quotient map of topological spaces that is not universally quotient than: x.com/gro_tsen/statu…
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Screenshot in previous post is taken from: Bentley, Herrlich & Lowen, “Improving Constructions in Topology”, p. 3–20 in: Herrlich & Porst (eds.), “Category Theory at Work (Bremen, 1990)”, Heldermann (1991).
Let X = ℝ as a topological space, and Y = ℝ / (id ∪ ℤ²) be the quotient topological space obtained by identifying all integers. Then X → Y is by definition a quotient map, but X × ℚ → Y × ℚ is not a quotient map! 😱🤯 pic.x.com/fQfaaUQ008
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@laurentbercot 🤯
I am henceforth adopting “the only free cheese is in the mousetrap” as my standard metaphor to explain why so many things online are free. bsky.app/profile/sjblak… pic.x.com/gnttZmOipK
On est arrivé au point où non seulement le niveau d'attention humain est tombé tellement en-dessous de celui des poissons rouges que 4 tweets de 280 caractères est jugé «trop long», mais en plus certains éprouvent le besoin de s'en vanter (plutôt que juste… ne pas lire). 😓 pic.x.com/22EkG2zcq2 x.com/gro_tsen/statu…
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@laurentbercot Je veux bien qu'on exclue n'importe qui du champ de la gauche, mais dans ce cas il ne faut pas revendiquer le nombre de leurs électeurs quand on chercher à faire valoir sa légitimité dans une démocratie.
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… (ou, pour ⓑ: pas d'extrême-droite) mais que l'appareil du parti trahit leurs volontés.␤␤Mais ça revient à prendre les électeurs desdits partis pour des idiots, et cet argument risque de se retourner contre eux.␤␤•4/4
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… ⓐau moins 4 groupes parlementaires sont à gauche, et aussi que ⓑle centre-droit n'est pas d'extrême-droite.␤␤Les deux semblent parfois poser problème.␤␤Les plus malins s'en tirent en expliquant que les électeurs de tel parti sont de gauche …␤␤•3/4
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Or en démocratie, réduire son propre camp à la portion congrue n'est pas génial pour défendre sa légitimité!␤␤Notamment, dans l'Assemblée nationale 🇫🇷 actuelle, si la gauche veut prétendre être 1re force politique, elle doit accepter de reconnaître que …␤␤•2/4
Toujours fasciné par la propension de gens se réclamant de gauche de se faire gardiens de pureté idéologique par des anathèmes excluant de la «gauche» tout désaccord sur ceci-cela.␤␤•1/4
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(This is from Michael, “Bi-quotient maps and cartesian products of quotient maps”, ‘Ann. Institut Fourier’ 18 (1968) 287–302 numdam.org/item/AIF_1968_… example 8.3.)
I am told this is an example of a hereditarily quotient map of topological spaces that is not universally quotient (=bi-quotient): let Y=[0,1] and X be the disjoint union of all convergent sequences in Y, and f:X→Y be the obvious quotient map.
I asked a long and rather rambling question on MathOverflow about what convergence spaces, pseudotopological spaces and pretopological spaces are good for, and what is the big picture to keep in mind about them. mathoverflow.net/q/497696/17064
RT @ArmyBarber: IQ is an excellent indicator of intelligence. The moment you hear someone talking about theirs you know you're dealing with… x.com/adot666/status…
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@chrsnjk I don't intend to commit this version.tex file, and I only ever commit things manually so I don't need a .gitignore file, but, yes, that's the idea.
I want to reliably ensure that a certain Git repository always contains a file “version.tex” with the output of the command: “git log --pretty=format:'\verb=%h %ad=' -1”␤␤Which Git hook(s) should I use for this? post-commit and post-checkout, I guess, but what else?
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@MadoreGene9434 x.com/gro_tsen/statu…
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… and adjust the checksums in build/pkgs/libsemigroups/checksums.ini to match the ones of the repackaged file. Then compilation seems to proceed as expected. 😌
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… as default, probably the reason for the problem) when the build script tries to unpack it. Of course this breaks the entire build.␤␤‣ Ugly workaround: extract libsemigroups-2.7.3.tar.gz and repackage it, replace upstream/libsemigroups-2.7.3.tar.gz by the repackaged file, …
Trying to compile sage-10.6 (from sagemath.org) on Ubuntu 20.04 LTS and ran across a super annoying build problem: libsemigroups-2.7.3.tar.gz fails to extract because of a utf8 decoding error (‽😕) in /usr/lib/python2.7/tarfile.py (this system still has Python2.7 …
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@EnergyThen Oui, et comme l'archi est archaïque c'est fait n'importe comment: au lieu que l'autorisation soit faite a priori en communiquant uniquement avec le site de la banque, elle est faite a posteriori, avec tous les problèmes techniques et légaux que ça pose. C'est absurde.
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Mais comme les banques sont coincées dans un système archaïque où le prélèvement se fait par simple numéro de compte/carte, avec contestation éventuelle a posteriori, on est obligé de tenir son numéro de compte ou carte bancaire secret, ce qui est fondamentalement absurde. •8/8
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Le risque de fraude en ligne serait réduit: pour acheter chez ACME point com je crée une autorisation (révocable!) de débiter mon compte de juste tel montant, juste vers le compte qu'ACME aura précisé, avec le numéro de commande en donnée annexe. Pas trop grave si ça fuite! •7/8
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Ce même système hyper simple («j'autorise le débit, je donne le numéro, l'autre effectue la transaction») pourrait servir pour abonnements, paiements en ligne, règlements entre particuliers, etc.␤␤Impossible de prélever d'un compte sans autorisation enregistrée! •6/8
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‣ Le titulaire du compte débiteur communique ce numéro au titulaire du compte à créditer, qui peut alors demander à sa banque de tirer tel montant.␤␤‣ La transaction est acceptée par les banques si le numéro est bon et le montant conforme aux contraintes prédéfinies.␤␤•5/8
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‣ Ce numéro peut bien sûr être échangé par toutes sortes de moyens, notamment comme un QR-code ou comme un lien.␤␤‣ La banque peut aussi enregistrer des données annexes pour le créancier et/ou le débiteur, comme un numéro de transaction.␤␤•4/8
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‣ La banque tenant le compte débiteur enregistre l'autorisation. Elle lui attribue un numéro confidentiel avec l'identification du compte + clé de sécurité. Le titulaire du compte peut la révoquer à tout moment (sauf cas très particulier des ordres irrévocables).␤␤•3/8
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‣ Cette autorisation est paramétrable et permet de tirer un certain montant maximal, soit une seule fois soit avec une certaine fréquence, soit à n'importe qui la reçoit, soit uniquement vers un certain compte. La somme peut aussi être séquestrée.␤␤•2/8
Voici cmt les virements bancaires devraient se faire si l'archi logicielle des banques n'était pas restée coincée dans les années 1960: 🧵⤵️␤␤‣ Le débiteur va sur le site Web de sa banque, ou, au-delà d'un certain montant, au guichet, créer une «autorisation de débit».␤␤•1/8
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@laurentbercot The point is that one understands people of one's age or generation better, so as one gets older one thinks young people are idiots whereas previously it was the older ones who were idiots.
The terrible thing about the passage of time is that old people stop being idiots while young people become more and more so.
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This is particularly noteworthy in the context of entrepreneurship, where ppl typically only observe ventures that succeed: but if you're rich you can afford to fail N times before you do something that works, whereas if you're poor, your first failure will be the the end of you.
The thing about being rich isn't so much the amount of stuff it lets you buy as the number of mistakes it lets you make without utterly ruining your life.
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Ça ressemble à un problème de Gettier: le poussinet a conclu a une fuite parce que les symptômes ressemblaient à ceux d'une fuite, et il en a trouvé une, mais elle n'était p-ê pas la cause des symptômes. Doit-on dire qu'il «savait» qu'il y avait une fuite? en.wikipedia.org/wiki/Gettier_p…
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Plot twist: le compresseur a été changé (€€€😢), mais peut-être que la fuite n'était pas, ou pas totalement, responsable de notre problème. On soupçonne maintenant (aussi?) un capteur de température défectueux dans une des unités intérieures.
RT @EUCourtPress: #ECJ #AG Medina: The dismissal of an employee by a Catholic organisation for leaving the Catholic Church may amount to di…
Try playing this little game: pick the grumpiest, crabbiest, person you encounter on a regular basis, and give yourself the mission to make that person smile (bonus points if they laugh).
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@ngspiensfr Interesting compromise between platonism and formalism! xkcd.com/690/
If you put BB(643) ultrafinitists in a room, do they get into a fight about who gets to use the limited resource of natural numbers?
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I posted a third answer to my own question on MathOverflow, using a computability retelling of Rosser's argument: mathoverflow.net/a/497405/17064␤␤For a hopefully somewhat understandable explanation of what is going on, see this long thread: x.com/gro_tsen/statu…
Do numbers exist even when nobody is computing with them?
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So the moral of the story is that by being smart, we can use theoremhood in any consistent theory T as above, to correctly decide which programs halt, even though T may (like PA♠︎ above) make false (=unsound) claims because its axioms are wrong. ✨ Truth from lies! ✨ •44/44
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… whether x terminates, we do not naïvely ask whether “x terminates” is a theorem of T; instead, we ask whether “t terminates” is a theorem of T, where t is the bizarre “Rosser” program defined in 34–36 above. This will happen iff x terminates (but not iff t does! 🤯). •43/44
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Claim proven! So what does this give us? Well, if we have a magic “T-theoremhood-oracle” that tells whether a statement (or just a Σ₁ statement) is a theorem of T, we can use it to decide whether a program x halts EVEN THOUGH T CAN BE UNSOUND (like PA♠︎): to decide … •42/44
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In the first case, x terminates, so we are done. In the second case, an execution trace of t will show it reaching an explicit endless loop, so T proves “t does not terminate”, and since T is assumed consistent, it can't also prove “t terminates”, a contradiction. ∎ •41/44
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Now for the converse [⇐]. Assume T proves “t terminates”. Again, there are two cases: either x terminates (in ①) before ② finds a proof of “t terminates” in T, or ② finds such a proof (which we just assumed exists!) first. •40/44
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[Note: the rather mind-boggling fact, here, is that in the second case, t DOES NOT terminate 🤯, since t runs an infinite loop in this case: that is, T is WRONG about “t terminates”. But remember, we're applying all of this to a theory that may be unsound, like PA♠︎.] •39/44
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In first case, t terminates by construction of t, so T proves “t terminates” by giving an execution trace of t (recall post 9 above! this still holds in T). In second case, ② found a proof of “t terminates”, so this proof exists: T proves “t terminates” as claimed. •38/44
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Here's the amazing thing about t:␤␤‣ CLAIM: x terminates if and only if T proves “t terminates” [yes: t not x!].␤␤Proof: [⇒] Assume x terminates. There are 2 cases: either x terminates (in ①) before ② finds a proof of “t terminates” in T, or ② finds such proof first. •37/44
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… if ① terminates first (i.e., if x terminates before ② finds a proof of “t terminates”), then: t terminates; but if ② terminates first (i.e., if it finds a proof of “t terminates” before x terminates), then: t enters an explicit endless loop (yes, this is strange!). •36/44
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… (this self-referential use of “t” in the definition of t is unproblematic by the standard “Cantor/Gödel/Quine trick”, aka “Kleene's recursion theorem”. I wrote a Web page ages ago madore.org/~david/compute… explaining this in detail, so I won't elaborate here); … •35/44
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Given a program x, we will let t be the following (weird!) program: ①on odd steps it runs the program x, but in parallel, ②on even steps it searches for a proof, in the theory T, of the statement “t terminates”, where t is the program that we're constructing (itself) … •34/44
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The clever trick, known as “Rosser's trick” is this: if you want to know whether a program x terminates, instead of asking whether “x terminates” is a theorem (I just explained why this doesn't work), you concoct a different statement/program, as I will now explain. •33/44
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In fact, this clever trick works not just for PA♠︎, but for ANY theory T that contains PA, is consistent (viꝫ. does not prove 0=1) and “computably axiomatizable” (essentially: an algorithm can decide whether a proof is valid). So let T be just that (e.g., PA♠︎). •32/44
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Now my MathOverflow question was essentially: can we still somehow use a “PA♠︎-theoremhood-oracle” to tell us true things about whether programs terminate (Σ₁ statements) despite the unsound axiom in PA♠︎. And answer is: yes we can! But it requires a clever trick! •31/44
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… namely the program z that searches for a proof of 0=1 in PA. So if we ask the “PA♠︎-theoremhood-oracle” whether “z terminates” is a theorem of PA♠︎, it will say “yes” because “z terminates” is the axiom ¬Con(PA) of PA♠︎. But in reality, z never does terminate.) •30/44
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So we can't decide whether x terminates merely by asking whether “x terminates” is a theorem: this will sometimes returns a wrong answer. (Recall that there is an AXIOM of PA♠︎ which falsely claims that some program terminates even though in fact it doesn't: … •29/44
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Specifically: can we use this magic “PA♠︎-theoremhood-oracle” to decide which programs terminate?␤␤In the case of PA, we were able to do this by asking whether “x terminates” is a theorem (of PA): this is true iff x actually terminates. But PA♠︎ has an unsound axiom! •28/44
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Now let me finally get to the point: some perverse genie gives you a magic device (a “PA♠︎-theoremhood-oracle”), that, given a statement of arithmetic, magically tells you whether the statement is a theorem of this (wrong!) theory PA♠︎. Can we do useful stuff with it? •27/44
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So we have this strange theory PA♠︎ := PA + ¬Con(PA) that adds an unsound axiom to PA, claiming that PA is inconsistent (so in particular, that PA♠︎ itself is inconsistent!), yet it is NOT inconsistent, it is just wrong. Wrong but consistent. •26/44
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(The reason the theory is consistent is this: deriving a contradiction from PA and the extra axiom “¬Con(PA)” that says “PA is inconsistent” is the same as being able to prove “PA is consistent” in PA, and Gödel tells you you can't do that.) •25/44
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… this axiom ¬Con(PA) is FALSE (in the natural numbers) because PA is, in fact, consistent. But, amazingly, adding this axiom to PA doesn't cause a contradiction (EVEN THOUGH IT CLAIMS THAT THERE IS ONE! 🤯), and this is again due to Gödel's incompleteness theorem. •24/44
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How can such a theory even exist? Well, here's an explicit example: add to PA an axiom “¬Con(PA)” that says “PA is inconsistent”; precisely, this axiom says: “the program that searches for a proof of 0=1 in PA will find one [it will terminate]” (so it's a Σ₁ axiom); … •23/44
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Now here is where things become strange: we will now imagine that I add to Peano arithmetic some axioms that are FALSE (of the natural numbers) but NOT CONTRADICTORY. So we get a theory that is UNSOUND but still CONSISTENT. Bear with me for a while. •22/44
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(Note that for more complicated arithmetic statements, “being a theorem of PA” and “being true of the natural numbers” can differ: the key point — that I repeated many times by now — is that for Σ₁ statements, they coincide: see post 11.) •21/44
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… whether a given program x halts (as usual: on a given input): just ask the oracle whether “x terminates” is a theorem. (And since this cannot be done algorithmically, cf. post 3 above, we conclude that our oracle must indeed be magical.) •20/44
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‣ To put it differently: if we had a magical device, let's call it an oracle, precisely, a “PA-theoremhood-oracle”, that, given a statement of arithmetic, magically tells us “this is a theorem of PA” or “this is not a theorem of PA”, we could use this device to decide … •19/44
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(In fact, conversely, the former would let us do the latter, because we could decide theoremhood by writing a program that tries all possible proofs until it finds one that works, and asking whether it eventually terminates. But concentrate on the other implication now.) •18/44
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… in fact, it is EXACTLY as hard as deciding whether something is a theorem, precisely for this reason: we can't algorithmically decide whether a program terminates, SO we can't decide whether something is a theorem, because the latter would let us do the former. •17/44
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❧ OK, I meandered off course a bit here, but let me get back to it. Our goal is to decide whether a program x halts. As I pointed out above (post 11), this is the case IFF Peano arithmetic proves that it does. Sadly, deciding whether something is a theorem is hard, … •16/44
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PA is sound, in particular it is Σ₁-sound, and in particular it is consistent. All these facts are true (they can be proved in set theory ZFC), but PA itself cannot prove them (it can't even state the first and can't prove the last two), a form of Gödel's theorem. •15/44
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OK, now let's look at a very special statement: “0=1”. This is (trivially) false, so a special form of soundness is that PA can't prove this. This very limited form of soundness is called “consistency”. It says that the theory doesn't collapse to absurdity. •14/44
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… But there are programs that do not terminate yet PA can't prove that they don't. One such is the program that tries to find a proof of 0=1 in PA: it will never find one, but PA cannot prove this — a form of Gödel's incompleteness theorem. I'll return to this below.) •13/44
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(What about programs that do NOT terminate? Well, if PA proves that a program does not terminate [← this is a “Π₁ statement”], then this program indeed cannot terminate, because this would prove a contradiction in PA and there is none as I'll say in a minute. … •12/44
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✱ To summarize: a program terminates (always: on a given input) IFF Peano arithmetic proves that it does. The “if” is Σ₁-soundness of PA, the “only if” is a trivial but crucial fact (that does NOT require soudness).␤␤Keep this in mind for all that follows! •11/44
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… then one can witness this fact by providing a complete execution trace of the program and saying “this execution trace follows the instructions, and it is finite, so the program terminates”, and this proves it. Again, this is almost trivial, but absolutely crucial. •10/44
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What about the converse? Well, if a program terminates, then PA (and much less) proves that it terminates; this is a very simple fact, but absolutely crucial in many parts of logic and computability: it is true simply because if a program terminates (on some input), … •9/44
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In particular, if PA proves that a program terminates (as always: I mean, “terminates on a given input or initial conditions”), then this program does, in fact, terminate: this special case of soundness is known as Σ₁-soundness (of PA). •8/44
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Peano arithmetic PA is “sound” in the sense that whenever it proves something, then that thing is true (of the natural numbers). This fact itself is actually subtle, and can't be proved, or indeed even stated, in PA itself, but it is a theorem of set theory (ZFC). •7/44
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(The theory we're talking about is precisely “first order” Peano arithmetic because it's written in a mathematical logic called “first order logic” (FOL). The only thing that really matters here is that proof-checking in FOL can be performed algorithmically.) •6/44
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One usual framework for proving things about arithmetic is “[first-order] Peano arithmetic” or just “PA”. This includes some basic axioms about +,×,↑ on natural numbers en.wikipedia.org/wiki/Peano_axi… including some ability to do mathematical induction (skipping details here!). •5/44
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Now what we usually do in mathematics is try to prove things. Statements of the form “program x terminates in finite time” are known as “Σ₁ arithmetical statements” (“arithmetical” because we can encode the behavior of the program in the language of arithmetic). •4/44
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One major and foundational theorem of computability theory (essentially due to Turing) is that the halting problem is not computable: no algorithm whatsoever can systematically decide (always in finite time) whether another algorithm terminates. •3/44
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So, the type of questions we're interested in here are those of the form “does program x halt?” (“halt” means: “terminate [in finite time]”; maybe on some input y but we can forget about it). This is known as “halting problem” in computer science. en.wikipedia.org/wiki/Halting_p… •2/44
Let me try to explain in a (slightly) less technical way what my question meant and what the answers I received from @JDHamkins and Emil Jeřábek tell us. Very long thread ahead (but I hope it is instructive)!␤␤«How to get mathematical truths from theories that lie.» 🧵⤵️ •1/44 x.com/gro_tsen/statu…
Don't believe in miracles: rely on them!
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To summarize the conclusion, though, the answer to the more general question is “YES”: we can computably extract the truth on halting of Turing machines from an oracle of theoremhood for ANY consistent recursively axiomatizable extension of PA, using a variant of Rosser's trick.
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… answers this more general question, and Emil Jeřábek provided another of his own. (MathOverflow is wonderful!)␤␤Now I have to approve either JDH's very nice explanations or EJ's brutally efficient and general argument, and I feel like Paris having only one apple to award. 😅
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‣ Update: my question was valid, but part based on a confusion of mine (now fixed). What I really ❋should❋ have asked is whether EVERY consistent recursively axiomatizable extension of PA is creative. But @JDHamkins wrote an answer 🔽 which actually … x.com/JDHamkins/stat…
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@KyleKulinski Any sufficiently advanced stupidity is indistinguishable from satire. x.com/gro_tsen/statu…
I asked a question on MathOverflow about “creative” theories of arithmetic: namely, theories from which you can computably decide whether Turing machines halt. Is Peano arithmetic + the axiom “Peano arithmetic is inconsistent” creative? mathoverflow.net/q/497307/17064
RT @KyleKulinski: pic.x.com/25aw7PuaOm
2395 years ago today, incidentally. x.com/gro_tsen/statu…
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PS: x.com/gro_tsen/statu…
I don't know who made this 🔽 meme, but as far as I'm concerned, it is absolutely perfect.␤␤(Also, one of the two, not necessarily the one you think, is f😚cking the other, and they're both enjoying it immensely.) pic.x.com/a3BIREmndT
“The train, in America, is not a choice. It is a punishment for, having neglected to read Weber on the Protestant ethic and the spirit of capitalism, making the mistake of remaining poor.”␤␤— Umberto Eco, ‘How to travel with a salmon’, 1994
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(The weather engineering is a reference to this 🔽, btw.) x.com/gro_tsen/statu…
Did you notice? Conspiracy theorists like to blame everything on Bill Gates, from microchips in covid vaccines to weather engineering. But when people get killed by WINDOWS, nobody even mentions his name in connection.␤␤Is someone investigating Bill Gates? 🤔 x.com/DarthPutinKGB/…
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I think I'm going to use the phrase “any sufficiently advanced stupidity is indistinguishable from satire” a lot. I honestly can't tell if this is parody:␤␤[tweet id: 1941567170728853677] pic.x.com/KujW076n9F
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@BallouxFrancois youtube.com/shorts/cB9BB-3…
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@BallouxFrancois Admit it: the thing that really got at you was how he thought you were French. 😁
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But if you want to show something American that the European mind could never comprehend, you can do better than people having fun in a pool. Try something like this instead: x.com/kidrock/status…
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@RepMikeCollins x.com/gro_tsen/statu…
Can I play this game too? Like, take a few clichés of Europe and write “the American mind could never comprehend”? pic.x.com/LC8ijexWAr x.com/RepMikeCollins…
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@BallouxFrancois Already an occasion to use my newly coined saying: x.com/gro_tsen/statu…
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… because we can be absolutely certain that law enforcement agencies will send their own goons to state the contrary. So if you have any kind of serious and believable credentials in cryptography, please consider participating!
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… will be an absolute disaster from the security point of view, and is impossible to reconcile with any form of privacy. We need to have all kinds of experts, from academia and industry, to state this very clearly, …
Europeans with credible expertise in cryptography and/or computer security should participate in this call by the 🇪🇺 Commission to explain to them, in terms that politicians can understand, why providing access to communications data to law enforcement … berthub.eu/articles/posts…
Your conscience never stops you from doing anything. It just stops you from enjoying it.
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@Dr_S_Sydoryk Not that I know. I just thought of it, but I'd be surprised if I were the first.␤␤Of course there are many examples along the “any sufficiently advanced <foo> is indistinguishable from <bar>”.␤␤I also recently proposed this: bsky.app/profile/did:pl… pic.x.com/LUBRo21mFM
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Also being discussed on Reddit: reddit.com/r/math/comment…
Nice question on Math Overflow: if f : ℝ^n → ℝ is assumed differentiable and |∇f| continuous, does it follow that ∇f is continuous? (I posted an easy partial answer in the case n=1.) mathoverflow.net/q/497234/17064
Any sufficiently advanced stupidity is indistinguishable from satire. quora.com/Why-do-Brits-s… pic.x.com/pPbBEgUZvz
Chaque année je suis surpris et agacé par la vitesse à laquelle la France passe de «c'est la fin de l'année scolaire, plein d'activité, même limite la panique pour tout finir à temps» à «c'est l'été, c'est fini, il ne se passe absolument plus rien, tout le monde est parti».
Many fear that Republicans are destroying American democracy but, fear not!, brave Democrats are rising to the occasion, taking on hard battles, defending the oppressed, fighting the worst of Trump's legislative agenda by… <checks notes> …getting the name of the bill changed. x.com/SenSchumer/sta…
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Et à un moment, il faut bien se rendre compte que les pompes à chaleur électriques sont de loin le meilleur moyen pour chauffer les habitations quand il fait froid, donc on aimerait bien en avoir partout… et que la situation est symétrique chaud/froid: les PàC sont réversibles.
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Ici, la meilleure façon de démonter une bonne partie de ces postures ou arguments qu'on peut qualifier de luddites est de regarder comment elles tiennent quand on remplace «clim» par «chauffage» (ou «pompe à chaleur»). Car personne n'est «anti-chauffage». x.com/gro_tsen/statu…
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… or il n'y a pas de façon plus efficace de rendre la société incapable d'avoir un débat sensé que d'arriver à créer une polarisation de toutes pièces (souvent sur le modèle de l'axe gauche-droite: être pro-X devient «de droite» et anti-X «de gauche» 🤦). x.com/gro_tsen/statu…
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… pour ça il y a urgence a développer le marché des clims au propane).␤␤Mais quand on voit ces arguments un peu sérieux mélangés à un florilège d'éléments de langage stéréotypés, on se dit qu'on n'est plus face à un débat rationnel mais du posturing politique («c'est Mal»): …
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Il y a bien des arguments qui méritent qu'on s'y attarde (le plus sérieux est celui des îlots de chaleur urbain, qui plaide à mon avis pour des clims collectives bien posées avec compresseurs sur les toits; un autre qui se tient est celui du fluide utilisé dans le compresseur: …
Je vois passer tant d'arguments «anti-clim» ultra idiots que je soupçonne que qqn de con a dû dire un truc «pro-clim» est qu'on est face à une de ces polarisations absurdes du débat politique où comme X a dit Truc, Y se précipite pour dire non-Truc. … x.com/gro_tsen/statu…
RT @bortzmeyer: L'Internet des Objets, c'est quand on peut passer root sur une ampoule électrique en envoyant du JSON. https://t.co/9sSzVDX…
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Previously: x.com/gro_tsen/statu… x.com/gro_tsen/statu…
I asked a question on the Computer Science Theory StackExchange about a presentation of Turing reduction that I've been thinking on and off for several months now. cstheory.stackexchange.com/q/55511/17747
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Bon, le technicien est passé et la fuite est irréparable. Il va falloir changer l'unité. 😭 bsky.app/profile/conscr…
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Et les records de froid à Paris, alors? Ça ressemble à ça ⬇️ Mais plus des deux tiers de ces records, dont quasi tous ceux du graphe de droite, représentent un seul événement: l'incroyable vague de froid de décembre 1879. 🥶 pic.x.com/Dup12zMPhP
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@letonyo Les données que j'ai prises s'arrêtent à mercredi dernier, mais pour l'instant on n'y est pas du tout. On risque éventuellement de batter un record de minimale quotidienne pendant les 1 ou 2 nuits qui viennent.
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Difficile de dire la “pire canicule”, et je ne sais pas cmt montrer la date à chaque fois. Mais les années revenant le plus souvent sont: 2003 (92 records), 1976 (54), 1911 (51), 2018 (24), 2006 (12), 1997 (12), 2022 (11), 2019 (8).␤␤Données brutes ici → gist.github.com/Gro-Tsen/74a07…
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Je pense que ça illustre bien la difficulté à définir un «record de chaleur»: je viens d'en donner 45×6 = 270 différents, juste pour Paris.␤␤Les courbes du 1er graphe tombent plus vite que celle du 2e car un seul jour un peu frais suffit à casser la série.
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Quant au point vert à (11 jours, 30.1°C) sur le second graphique, il signifie qu'il y a eu 11 jours consécutifs sur lesquels la température moyenne quotidienne, moyennée sur les 11 jours, a été de 30.1°C, et que c'est le record (en l'occurrence, du 2003-08-03 au 2003-08-13).
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Par exemple, le point bleu à (14 jours, 20.5°C) sur le premier graphique signifie qu'il y a eu 14 jours consécutifs dont la température minimale quotidienne est descendue au plus bas à 20.5°C, et que c'est le record (en l'occurrence, ça s'est produit du 1976-06-24 au 1976-07-07).
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… celui de droite donne les records de moyenne pendant n jours consécutifs.␤␤Chaque graphique a trois jeux de points: un pour les maximales quotidiennes, un pour les moyennes quotidiennes, et un pour les minimales quotidiennes.
J'ai calculé tous les records de chaleurs sur n jours consécutifs, pour 1≤n≤45, à la station de Paris Montsouris. ⬇️␤␤Voici comment il faut les lire: le graphique de gauche donne les records tenus sans arrêt pdt n jours consécutifs (i.e., les records max du min sur n jours), … pic.x.com/onX2VyIQlJ
“What was Doctor Presume's full name?“␤␤“Doctor Livingstone I. Presume?”␤␤(Sorry.)
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(C'est une version beaucoup plus détaillée de ce fil: 🔽) x.com/gro_tsen/statu…
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Plus d'explications/commentaires dans mon blog: 🔽␤␤PS: deux skeets plus haut, il y a une erreur de lecture sur la ligne.␤␤x.com/gro_tsen/statu…
Où je profite du prétexte d'un jeu de données sur la température à Paris Montsouris pour parler du maximum et du minimum en maths, et du théorème du minimax… mais surtout pour m'amuser avec les données en question. madore.org/~david/weblog/…
RT @ngspiensfr: @JohnPSharpe @fiordiligi76 @AgChristie2 Toute forme d'art va, au fur est à mesure que des artistes talentueux s'en emparent…
RT @AFP: 🏳️‍🌈 A record number of people are expected to attend Saturday's Pride march in the Hungarian capital Budapest, defying a ban from…
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@BrantonDeMoss @JDHamkins We can easily do an experiment that tests something that ZFC, if consistent, cannot prove: run a program that searches for a contradiction in ZFC. And we readily accept, sometimes adding as axiom, the (wildly believed) conclusion that it will not find one. (Repeat ad lib.)
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@laurentbercot À tes yeux peut-être, mais tu n'es pas un de ceux qui défilaient tout à l'heure.␤␤(Bon, après, c'est très bien que la gay pride soit un truc de jeunes. S'il n'y avait que des boomers, je me sentirais jeune mais ce serait aussi flippant.)
Bon, regarder les mecs jeunes et beaux défiler à la gay pride c'est rigolo quand on est soi-même jeune et beau (enfin, pas trop laid). Mais quand on est devenu vieux, moche et aigri, c'est juste frustrant. Il n'y a plus qu'à prétendre que «c'était mieux âvant».
Une illustration de pourquoi il ne faut pas faire des stats sur les extrêmes mais sur des moyennes: les températures relevées à Paris-Montsouris avec, pour chaque année (de septembre à août) le maximum, le minimum, et la moyenne annuelle. Le 2e graphe zoome sur la moyenne. pic.x.com/bcAmeHQQl3
DID YOU KNOW that one popular way of counting dates in astronomy (the “Modified Julian Date”) is to count the number of dates that have elapsed since the foundation of Denver, Colorado? (Ha, ha, only serious.) en.wikipedia.org/wiki/Julian_day
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@CertumIter Je conseille plutôt de faire un tour des installeurs de clims domestiques. 😁
So apparently someone took Hilbert's “Infinite Hotel” paradox en.wikipedia.org/wiki/Hilbert%2… and made it into a computer game called “Hotel Infinity”. youtube.com/watch?v=OzAh3p…␤␤(I have no idea whether it's good. I can't play games on my computer.)
C'est peut-être le moment de rappeler que le mensuel “Le Point” a trouvé le moyen de publier, en 2019, une colonne intitulée «Canicule: faites un tour en voiture pour prendre un “coup de frais”» 🫠 lepoint.fr/automobile/can… pic.x.com/3LqHzMuoKD
RT @katherineveritt: Foucault: pic.x.com/2bhLCWwPAU x.com/tr3nchc04t/sta…
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Mais on peut aussi permuter le calcul sur l'année et le calcul sur le jour: ⬇️␤␤Cette fois, la ligne min(max(moy))=10.9 signifie que le 29 janvier est le jour qui a le plus petit maximum (sur toutes les années) de la température moyenne (sur la journée), atteint en 2013. pic.x.com/RWDhmD9QuN
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Ça donne ça: ⬇️␤␤Par exemple, la ligne min(max(moy))=15.8 signifie que l'année 1874–1875 est celle qui a le plus petit maximum (sur l'année) des températures moyennes (sur la journée), et qu'il vaut 15.8°C, atteint le 18 août 1875.␤␤Version texte ici: gist.github.com/Gro-Tsen/74a07… pic.x.com/VnIYHPr2lb
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La source des données est là: meteo.data.gouv.fr/datasets/donne… (fichiers “Q_75_1816-1949_RR-T-Vent.csv.gz”, “Q_75_previous-1950-2023_RR-T-Vent.csv.gz”, et “Q_75_latest-2024-2025_RR-T-Vent.csv.gz”).
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(Je précise aussi que mes années vont du 1er septembre au 31 août, de manière à ne pas casser en l'hiver en deux: ce serait idiot de ranger un record de froid le 31 décembre de manière différente d'un record de froid le 1er janvier: c'est le même hiver.)
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… minimum moyenne ou maximum sur le jour dans l'année, et minimum, moyenne ou maximum dans la journée (bon, avant 1950, la température moyenne de la journée, c'est juste (max+min)/2 parce que la vraie moyenne n'est dispo).
J'ai récupéré les températures minimales et maximales relevées par la station météo de Paris Montsouris depuis 1873 et j'ai calculé quelques minima, moyennes et maxima.␤␤Et quand je dis “qqs”, j'ai calculé les 27 combinaisons possibles: minimum, moyenne ou maximum sur l'année, …
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Le poussinet a trouvé la fuite de gaz dans la clim avec son détecteur, maintenant il sautille dans tous les sens en criant «J'AI TROUVÉ! J'AI TROUVÉ LA FUITE!» et en vitupérant contre les gens qui ont essayé de le gaslighter que c'était pas une fuite. bsky.app/profile/conscr…
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@prtsnf Ceci n'explique pas la différence entre (réactions par rapport à) chauffage et clim. Si l'argument est «il faut des maisons passives», il devrait s'appliquer au chauffage au moins autant que la clim. Or manifestement ici il y a différence de traitement.
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@NiluarO @chambergeot17 (Ce que je veux dire, c'est qu'on ne peut pas simultanément prétendre que la clim est un gâchis important d'énergie — ce qui suppose que l'usage est important dans l'année — et que c'est inutile parce qu'il n'y a que peu de jours très chauds. You can't have it both ways.)
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@NiluarO @chambergeot17 Aussi, s'il y a bcp moins de jours trop chauds que trop froids, ça explique tout à fait que certains préfèrent s'en accommoder que de s'installer une clim, mais ce n'est pas un argument sensé pour prétendre les interdire/réprouver: le prétendu «gâchis d'énergie» sera minime.
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@AlanVRK I'll ask my boyfriend's parents: they have flat in Majorca (and I'm pretty sure they have AC).␤␤Cc @Conscrit_Neuneu
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@PhilippeThomazo x.com/gro_tsen/statu…
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Pour rappel, une pompe à chaleur bien posée est qqch comme 3 à 5 fois plus efficace (pour apporter ou évacuer de la chaleur) qu'un chauffage traditionnel. Et en France, l'électricité est largement décarbonnée, surtout en été. madore.org/~david/weblog/…
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Il faudrait vraiment analyser l'origine de ce courant de pensée qui prétend que «rafraîchir son logement quand il fait trop chaud dehors» est un luxe frivole et un gâchis d'énergie, alors que PERSONNE ne le pense pour «réchauffer son logement quand il fait trop froid dehors».
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(Spoiler: le résultat est que les locataires achèteront des clims mobiles d'appoint, les installeront comme ils pourront à travers des fenêtres mal calfeutrées, et que le bilan énergétique sera beaucoup plus pourri qu'avec une PAC bien posée.)
Donc apparemment il y a des règles de certains bailleurs sociaux qui interdisent la clim, même quitte à bloquer la fonction «clim» d'une pompe à chaleur réversible (ne lui permettre de fonctionner qu'en chauffage), parce que la clim est une «dilapidation» d'énergie. 🤦 x.com/PhilippeThomaz…
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@laurentbercot … en difficulté on doit souvent découper en taille des pas, et ça fait des choses insatisfaisantes).␤␤Mais peut-être que j'ai tort de vouloir faire des problèmes qui visent à démontrer un résultat final un peu intéressant (après tout, les élèves s'en foutent sans doute pas mal).
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@laurentbercot … à très dur, pour avoir de quoi juger n'importe quel niveau (départager les mauvais des très mauvais et les très bons des bons): ça reste dur à concilier avec le découpage naturel d'une démonstration qui ne colle pas forcément à ce qu'on voudrait (donc faute de découper …
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@laurentbercot La disparité des niveaux est un problème, oui, et plein d'autres choses le sont (le manque de temps pour réfléchir posément, l'habitude de questions très formatées, etc.). Mais c'est de toute façon souhaitable de faire des questions dont la difficulté s'étale de très facile …
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@laurentbercot (Et quand je vois qu'un élève qui, à en juger par l'ensemble, est vraiment bon, a du mal sur une question des plus faciles, je me dis que c'est un problème de communication, pas de substance.)
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@laurentbercot Disons que dans certains cas, le découpage nécessaire à ce que les élèves les moins bons arrivent à faire quelques trucs fait que les meilleurs ont vraiment du mal parce qu'ils ne comprennent même plus ce qu'il faut dire pour certaines questions trop faciles.
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Ce qui est un peu triste, en fait, c'est que c'est les mêmes problèmes qu'aurait ChatGPT. 😬 (Parce que oui, ChatGPT, si on lui demande «prouver moi <truc>», il va toujours y arriver miraculeusement, et si <truc> est trivial, souvent il va sortir un truc tarabiscoté.)
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‣ Si on mâche les problèmes en tout petites questions faciles, il y en a toujours qui vont chercher midi à quatorze heures et écrivent des réponses inutilement compliquées ou tarabiscotées, ou des pages de justification. Si on ne le fait pas, ils n'y arrivent pas.␤␤…
Les dilemmes de l'écriture d'un sujet d'examen de maths:␤␤‣ Si on donne dans la question la réponse à trouver, les élèves arrivent toujours miraculeusement pile au résultat qui était demandé. Si on ne la donne pas, ça peut bloquer pour les questions suivantes.␤␤…
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J'ai fait le trajet Palaiseau ↔︎ Paris deux fois cette semaine (même température), une fois à moto avec casque intégral et équipement en cuir de la nuque aux pieds, et une fois en RER B, et je pense que j'ai plus transpiré dans le deuxième.
Pour convaincre les franciliens de prendre les transports en commun plutôt que leur voiture, peut-être qu'une bonne première étape serait d'avoir une CLIM QUI FONCTIONNE dans les RER comme dans toutes les voitures individuelles. Et pas juste dans une rame sur 10.
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Les notes du cours: perso.enst.fr/madore/mitro20…
Si ça intéresse quelqu'un, l'examen qui a eu lieu ce matin pour le cours de théories des jeux (“théories” au pluriel, merci) que je donne à Télécom Paris est ici: perso.enst.fr/madore/mitro20…␤␤Et le corrigé est là: perso.enst.fr/madore/mitro20… ❦
Au moins un petit avantage du déménagement du boulot à Trifouilly-lès-Saclay, c'est la cantine dehors quand il fait beau. pic.x.com/wiMQPkqIWQ
Tout le monde parle des pics de chaleur en température maximale, mais personnellement une nuit à 24°C mini me fait beaucoup plus peur qu'un jour à 40°C maxi.␤␤(Et en plus, ce qu'il faudrait vraiment donner, c'est la température de thermomètre humide.)
RT @LYMFHSR: En règle générale les étudiants n'ont pas l'air de comprendre ou de remarquer que si tu fais réécrire ton texte par un LLM il… x.com/LYMFHSR/status…
À toutes fins utiles, pour ceux qui ne connaissent pas déjà cette carte des impacts de foudre en temps réel, je rappelle l'existence de Blitzortung: map.blitzortung.org/#6/48.862/2.331
Les frigos ayant un compartiment congélation ont typiquement un seul thermostat, dans la partie principale, et le compresseur travail pour l'ensemble. Résultat: plus il fait chaud dehors, plus il fait froid dans le compartiment congélateur (pq le compresseur travaille plus).
Pigeons profitant de la fraîcheur d'un brumisateur pour les plantes. pic.x.com/wZzOsAohAF
I don't know if the Norwegian tourist was refused entry because of this meme or for some other reason that may or may not have been decided ex post facto, but one thing is certain:␤␤This image is now ALL OVER international news and social media. 😂 x.com/NewsWire_US/st…
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The total population of all the 100 cities in the database that are in this octant is around 400k. So it's pretty safe to say that well below 0.1%, probably even less than 0.01%, of the world population, live in the “south-west-back” octant. 😯
According to a database I found of all world cities with population >1000, the largest one in the “south-west-back octant” of the Earth (i.e., latitude ≤ 0° and longitude ≤ −90°) is: Apia, capital of Samoa, with a population of… around 40k people (Wikipedia says 36k). x.com/gro_tsen/statu…
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Also, the 90°E meridian separates India from the densely populated parts of China and South-East Asia, so it becomes interesting to see how the population divides. Conversely, the south-west-back octant seems to have a population of nearly 0.
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We can label the eight octants with all combinations of {north, south}, {east, west} and {front, back} depending on where they lie wrt the equator, the 0°/180° meridian and the ±90° meridian. Neat!
Please! If you're going to divide the Earth geometrically like that, at least do it following a regular solid: like, also divide at the ±90° meridians, giving 8 octants that are all equilateral and triple-right-angled triangles (a spherical octahedron). x.com/amazingmap/sta…
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I only skimmed through the actual thesis (supervised by Patrick C. Fischer), but the executive summary is that he defines and studies a programming language (“LOOP”), whose programs always terminate, that can exactly represent the α-th level of the hierarchy, for α < ω^ω. •4/4
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“Subrecursive hierarchies” (e.g., the Grzegorczyk hierarchy) are about bridging the space between the top of what people usually study in complexity theory (primitive recursive) and the bottom of what people usually study in computability theory (Church-Turing computable). •3/4
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There is some mystery around why he didn't get his degree and also, how the thesis was typeset. See dmrthesis.net/dmr-thesis/ for a very detailed exploration of the latter. An effort to recreate the document also made a computerphile video: youtube.com/watch?v=82TxNe… in 2021. •2/4
So apparently Dennis Ritchie (“DMR”, famous for inventing the C programming language and participating in the creation of Unix) wrote a PhD dissertation on subrecursive hierarchies at Harvard in the 1960's, but somehow never actually got his degree. computerhistory.org/blog/discoveri… •1/4
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✱ Note: in the statement of the theorem above, it is not required that the minimal programs generated do anything useful or interesting. We are just saying that the set of minimal programs, despite being infinite (why?) does not have any infinite computably enumerable subset.
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… Hint / sketch of proof:␤␤‣ If there were, one could (why?) find a computable function f such that, for all e, f(e) is some minimal program strictly longer than e. ␤␤‣ But by the Kleene-Rogers fixed point theorem, there is e such that f(e) behaves like e. Absurd! ∎␤␤.…
A fun result in computability (reportedly due to Carl Jockush):␤␤‣ Say that a program (=Turing machine) is “minimal” when there is no (strictly) shorter program that behaves identically.␤␤‣ Theorem: there is no program that generates infinitely many minimal programs.␤␤…
I wrote an answer on Math StackExchange explaining why (and how) one can find three random variables each following a standard normal distribution, any two of which are independent, but such that all three are NOT independent: math.stackexchange.com/a/5078249/84253
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@laurentbercot That's pretty much my point. Nobody writes physics like this, nobody should, nobody can reasonably read a formula like this, and this only serves to make it seem far more complicated than it really is.
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Obviously nobody writes or uses a formula like this. It was written to make a point. But what point, exactly? I seem to remember it was Alain Connes, but I don't remember why, and I'd like confirmation.␤␤I wrote this on Reddit: reddit.com/r/Damnthatsint…␤␤Can sbd confirm/correct? pic.x.com/9qFOJDD4hX
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An deconstruction of the formula is given here: symmetrymagazine.org/article/the-de… (if you actually want to learn about the Standard Model, I would recommend something like this: arxiv.org/abs/hep-ph/030… ). But that's not what I'm asking about.
A question on the history of the presentation of physics: does someone know where and when, exactly, this exact formula for the Standard Model Lagrangian appeared (which then went somewhat viral), and what the point was of writing out everything that way? pic.x.com/4vB5Aamdng
RT @haveigotnews: British media treats delicate Middle East situation with trademark nuance and respect pic.x.com/sjmMYctacT
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Or maybe she's some kind of radical leftist whose opinions should be distrusted on all matters relating to US national intelligence? 🤷 x.com/TulsiGabbard/s… pic.x.com/u2j9RhDYoK
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I mean, she seems pretty knowledgeable. Did she, perhaps, get her point across? x.com/TulsiGabbard/s… pic.x.com/PRKFkLMaJT
I wonder what became of the person who made this interesting analysis. 🤔 pic.x.com/Cch6ReE1Ex x.com/TulsiGabbard/s…
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@Sotorumuro Je l'ai aussi chez moi quelque part, mais je ne sais plus où il est passé.
Il semble qu'il eut existé à Paris, dans l'enceinte de Thiers, une porte de Bicêtre entre la porte d'Italie et la poterne des Peupliers.␤␤Quelqu'un saurait-il dire quel était son emplacement exact?
Même pour raconter un problème de clim je trouve moyen d'en écrire un roman, mais il est vrai qu'il y a pas mal d'indices qui viennent compliquer l'enquête: madore.org/~david/weblog/…
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@AlanVRK Sorry, I did notice it, and bookmarked it for later reading, but I was a bit busy with other things. But I do intend to get back to it, and I appreciate your taking the time to write it down!
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But while the algorithm convincingly answers the question of “how” the text was generated, I would also like to link to this excellent (if lengthy) video by ‘Esoterica’ on other aspects, including motivation and a material analysis of the book itself: youtube.com/watch?v=67YzIO…
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The reason I mention this now is that the ‘SciShow’ channel on YouTube published a video summarizing the case and discussing the paper of which the previous tweet shows a section: youtube.com/watch?v=K0wVcF…
For what it's worth, let me remind everyone that the case of the Voynich manuscript should be considered closed: it's a hoax — there is no mystery and no hidden meaning to find.␤␤We even know a plausible method (usable by hand) by which the random text might have been generated. x.com/gro_tsen/statu…
Funny thing about email is that it was conceived as a slow but reliable means of communication (servers will retry for days before they give up on delivery).␤␤But spam filters have made it unreliable, and we treat it as instantaneous (assuming mails will arrive within seconds).
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③ Are people living in a detailed simulation of a universe different from characters in a book? Are we different from either? How might we tell?␤␤④ Should we fear our own death any more than a book (or its characters) should fear its last page?␤␤⑤ Deep mystery or mumbo-jumbo?
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② Do they die when the book ends (if not before)? Does their entire world cease to exist? If so, ought they try to act so as to protract the novel?␤␤Also, when does this happen? At the last page in an abstract sense? When the author writes it? When each reader reaches it?
Random food for thought:␤␤① Are the characters in a novel conscious? (or are they “philosophical zombies”?)␤␤If not, how could they themselves know they aren't?␤␤If yes, do they live in the pages of the book itself? in the mind of the author? that of the reader(s)?
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@MadoreGene9434 Sur l'esplanade Gaston Monnerville (celle qui relie le Luxembourg à Port-Royal, dans l'alignement de l'Observatoire), au niveau du croisement avec la rue Michelet: openstreetmap.org/?mlat=48.84257…
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@IanSolliec It seems a press release on the causes of the blackout has been published by the Spanish government: mcusercontent.com/2702b812ce1f3e… with a full report to be released later.␤␤See also: arstechnica.com/science/2025/0…
Cynara cardunculus (artichoke / cardoon), used as an ornamental plant, in bloom, in the streets of Paris. pic.x.com/0nT96o3v42
RT @TW1NKD3STR0YER: man academia must evolve with the times pic.x.com/lgPD1Wkabn
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Server confirmed dead. Replacement server supposedly on its way. Will likely take some time for me to install and configure (I have backups of everything but this is still a pain).
Personal announcement: the server hosting my email seems to be down (probably dead for good, will need to reinstall a new one). So don't try to contact me by email for the next few days.␤␤(Not that I reply to email anyway, but now I can't even read it.)
RT @VK_HM: pic.x.com/uDy6JDJ9ZD x.com/bigmeaninterne…
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@fa4b_e Oui alors un mousqueton qui doit supporter des charges de dizaines de kilos pour la musculation, je pense qu'il vaut mieux qu'il soit en métal et je ne crois pas qu'on fasse de l'impression 3D de métal (enfin, pas à un coût compétitif aux méthodes tradi).
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OK, les gens n'arrêtent pas de les voler, soit. Mais même s'il s'en vole un par jour (et j'en doute), ça ne représente rien dans le budget d'un tel club de les changer illico, et ça représenterait un doublement de fait du nombre de poulies disponibles.
Ma salle de sport Neoness a des machines de musculation à poulies, qui doivent coûter €€€, dont la moitié sont fonctionnellement inutilisables parce qu'il leur manque un mousqueton pour raccorder la poignée, lequel doit coûter qqch comme 3€ (par côté) pour un modèle deluxe.
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@AlanVRK If you can sketch a proof¹ or ingredients of a proof of why ∀x∈C (f′(x) exists ⇒ f′(x)=1), I would be interested, because I don't see it.␤␤1. On whatever medium you find is appropriate, if it's too annoying to split in 280-char bites, of course.
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… And it's not just the AI-generated snippet which is wrong. I can't seem to scroll down far enough to find a page talking about Amo with this particular search query.
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… Well, Anton Wilhelm Amo (a fascinating character, born in what is now Ghana, and brought to Europe probably as a slave) obtained a doctorate from the university of Wittenberg in 1734. Last time I checked, 1734 < 1876. … en.wikipedia.org/wiki/Anton_Wil…
Interesting bit of US-centrism from Web search results. I was trying to remember the name of Anton Wilhelm Amo, so I searched “first black man to get a doctorate” then adding “in the world”. Basically all answers are about Edward Bouchet (Yale PhD in 1876) and other Americans. … pic.x.com/kIkvSrTuR5
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@AlanVRK … For example 0100111111000…0001… where the length of the n-th run of equal binary digits grows like n! (perhaps even faster) seems like a good candidate to have f′(x)=0. (Intuitively, because it is very well approximated ✳︎on either side✳︎ by the edges of the plateaux.)
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@AlanVRK My intuition agrees with yours on the first. I don't know what to think of the next two. But I have a different intuition for the last: I think a point x of C whose “binary expansion” alternates 0's and 1's in hugely increasing lengths will have f′(x)=0. …
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@AlanVRK I agree.
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@AlanVRK Yes, a characterization is going to be specific to this set. I expect something like “x∈C satisfies f′(x)=1 iff the number of 1's in the first n digits of the ‘binary expansion’ of x in C is bounded between [two explicit asymptotic bounds]”. This I would consider a full answer.
RT @Pierrepilleds: pic.x.com/OCwdXJb5ZD
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@AlanVRK … Basically anything beyond those three points is unknown to me, including:␤␤‣ What is the cardinality of the set of non-differentiability points of f? Its Haudorff measure?␤␤‣ Do there exist points where f′(x) exists but is strictly between 0 and 1? Points on C where f′(x)=0?
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@AlanVRK … And:␤␤‣ There exists an increasing homeomorphism φ such that φ∘f is differentiable everywhere (so, by changing the values on the “plateaux” we can make f differentiable, something I find very hard to visualize).␤␤(I posted a proof of this on MathOverflow.) …
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@AlanVRK …␤␤‣ f is not differentiable at the (countably many) edge points of the (countably many) intervals that are the connected components of the complement [0,1]∖C (at these points, one sided derivative is zero and the other is non-zero).␤␤…
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@AlanVRK … Basically all the things I know are this:␤␤‣ f is differentiable on the complement [0,1]∖C of C (where f′(x)=0) and at the set dens(C) of points of density of C (where f′(x)=1); the remaining points C∖dens(C) are measure zero.␤␤…
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@AlanVRK I had indeed briefly thought f were differentiable everywhere. This was a stupid computation error (in bounding the size of the k-th subdivision I thought I had concluded f′(0)=0), so I cancelled after re-checking that the left and right derivatives at 0 exist and differ. …
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@AlanVRK … But (as you do, I understand) I prefer to think of it as the cumulative function of the uniform probability measure on C rather than Lebesgue measure, so yes, there's a silly factor μ(C). I had hoped it would not cause confusion, but, well, 🤷.
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@AlanVRK I much prefer the second construction. The reasons why I defined it as x ↦ μ(C∩[0,x]) is that it's shorter to write/explain and that that (presumably for the same reason) is what the MathOverflow question did. So I reused the same convention. …
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@AlanVRK > It's not a homeomorphism␤␤Maybe I wasn't clear. It's a homeomorphism (and also an order isomorphism) between C (whether fat or thin) and {0,1}^ℕ with the product topology (and lexicographic order).␤␤Of course no longer when we change to [0,1] at source and/or target.
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@JacqBens Obviously that would be better (or perhaps per time driving), but the denominator in these kinds of stats is basically impossible to know, unlike the total population. Total number of vehicles might be another sensible compromise.
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@AlanVRK I suspect that f is not differentiable at points whose “binary expansion” in C consists of 1's that are very sparsely spaced between lots of 0's, but I don't know how to prove this. x.com/gro_tsen/statu…
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@AlanVRK So, if you wish, that makes at least countably many points where f is not differentiable, and we know that there are at most a measure zero set. The question is where, between the two, the set of non-differentiable points of f lies.
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@AlanVRK I agree that if x is an edge point of one of the intervals that are the connected components of the complement of C (equivalently, its “binary expansion” is eventually constant), then f is not differentiable at x (its one-sided derivatives are 0 and 1). But there may be others.
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@AlanVRK The questions are roughly as follows:␤␤① Given the “binary expansion” h(x) (cf. 🔽) of a point x in C, can we decide whether f′(x) exists? whether f′(x)=1?␤␤② Do there exist x∈C such that f′(x) exists but 0<f′(x)<1?␤␤x.com/gro_tsen/statu…
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@AlanVRK … In fact, the Sage code I used to draw both graphs is exactly the same except that I removed the scale factor in the thin Cantor case (and, of course, I changed the α parameter from 1/4 to 1/3).
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@AlanVRK … So this is what I meant: the function f being considered for the fat Cantor set can be considered (up to a scale) the staircase function defined by the second construction above, and this one works for both fat and thin cases. …
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@AlanVRK … But in the case of the fat Cantor case considered in this question (where at stage k we remove 2^(k−1) intervals of length α^k) these two constructions coincide up to a scale (namely μ(C)) because each twofold division is in equal parts. …
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@AlanVRK … equivalently, you take x ↦ λ(C ∩ [0,x]) where now λ is the pullback by h of the product probability measure on {0,1}^ℕ. For the usual Cantor set C this is the standard Cantor function that I drew on the right. …
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@AlanVRK … there is a natural homeomorphism h : C → {0,1}^ℕ such that the first k terms of h(x) which one of the 2^k level-k parts of C the point x lies in, and if you compose with summing binary expansions {0,1}^ℕ → [0,1] you get a continuous map C → [0,1] which extends to [0,1] …
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@AlanVRK If C ⊆ [0,1] is a Cantor-like set, there are two different ways to define a staircase function from C: one is x ↦ μ(C ∩ [0,x]), and I agree that for the usual Cantor set this is identically zero. But there is another way: …
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@JacqBens @RomainHedouin 😝 ourworldindata.org/grapher/death-…␤␤(I didn't know what to expect when I looked this up, and honestly I'm pretty surprised, because, from what I see, I would tend to agree with the assessment that “French people can't drive”.) pic.x.com/GwuKQ4Svyz
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@ngspiensfr (The thing about this point is that while it is not an edge point, it is still pretty damn close to them.)
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@ngspiensfr Here's the sort of points which might be problematic: identify points of C with infinite binary sequences where ‘0’ means “go left” and ‘1’ means “go right”.␤␤Is f differentiable at the point 0100100000010…010… where the number of 0's between two 1's grows like n factorial? 🤔
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The question is: at which points is f (of the left graph above) differentiable? Are there x such that 0<f′(x)<1?␤␤We know this: f′=0 on the complement of C (the “fat” Cantor set en.wikipedia.org/wiki/Smith%E2%…), and f′(x)=1 if x is a Lebesgue density point of C. That's about all.
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* Correction: the graph earlier in this thread is incorrect (should NOT be self-similar).␤␤The graph below left shows the function f we're talking about (for param α=¼).␤␤Right (⚠️ different scale!) shows standard (non-“fat”) Cantor set “devil staircase”. en.wikipedia.org/wiki/Cantor_fu… pic.x.com/8rpCwwa1ab
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@ngspiensfr The boundary of the fat Cantor set is the fat Cantor set itself (even though it has positive measure, it is still closed with empty interior).␤␤If by “boundary” you mean the (countable!) edge points of the connected components of its complement, then maybe. I don't know.
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@ngspiensfr (Except that I just realized that my graph is wrong, it should NOT be self-similar. 😖 BRB fixing my code.)
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@ngspiensfr So, on the left, the standard Cantor staircase function (normalized to total height 1), which is differentiable exactly on the complement of C and has derivative 0 there; and on the right, the one we're talking about, which has to be differentiable at some points of (the fat) C. pic.x.com/IWvPPd1dAt
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@ngspiensfr … (just like it is for the standard Cantor set), but this is wrong: a monotonic continuous function must be differentiable a.e., and since C has positive Lebesgue measure, there must exist points of C where it is differentiable.
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@ngspiensfr … here we use a “fat” Cantor set: we remove 2^(k−1) intervals of length α^k (with α < 1/3) at step k of the construction, so the final set C has Lebesgue measure (1−3α)/(1−2α) > 0. Now initially I thought, as you probably did, that f must be non-differentiable on C …
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@ngspiensfr The standard devil's staircase / Cantor function is for the standard Cantor set, where we remove a 2^(k−1) intervals of length (1/3)^k at each step, so the final set has Lebesgue measure 0 and the function is indeed non-differentiable exactly on C. But …
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@ngspiensfr … be differentiable unless f already were so. Combined with my erroneous computation that f′(0)=0 this made me think f must be differentiable everywhere, but in fact it's not. So I'm confused.
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@ngspiensfr … but it seems that squeezing to help at one point will necessarily make things worse at another (e.g. if you bring down the middle plateau you're helping the left part be differentiable, but making it harder for the right part), so I don't understand intuitively how φ∘f can …
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@ngspiensfr And what confuses me is this: I have proof that φ∘f can be differentiable everywhere; now intuitively, I can understand that φ helps makes helps at points where it squeezes the values gently so as to make (φ∘f)′(x) = 0 at the edge points of the plateaux, …
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@ngspiensfr … (Its derivative is 0 outside C, 1 a.e. on C, and of course it's discontinuous in many points.)␤␤But I thought I had persuaded myself that f′(0)=0 for the original function (as plotted, not just some φ∘f), and I realized that my computation was wrong, so I deleted that tweet.
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@ngspiensfr I knew (and remembered) that derivatives satisfy the intermediate value property, so if they take values 0 and 1 they must take all values in between. This is indeed the case for the function φ∘f (with φ homeomorphism) constructed in my MO answer. …
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I posted a partial answer on MO showing that, by left-composing f with a homeomorphism (so, essentially, by changing the heights of the “plateaux”) we can make it differentiable everywhere. 🤯␤␤But I don't know what to believe for the original f (plotted above). I'm confused.
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The most dangerous belief in the world is the idea that your country (or some other group you belong to) can do no wrong.
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… Because they are so secure in their belief that OF COURSE 🇺🇸America🇺🇸 is the Land of 👊Freedom👊, so OF COURSE their guy can't be a dictator or even act like one when he forbids demonstrations. America and dictatorships belong in ontologically different categories to them.
Americans have been so thoroughly indoctrinated in believing their country is the Land of the Free, that the guy can openly showcase the paraphernalia of military dictatorships, like holding a military parade on the Leader's birthday, and his supporters won't even blink. … x.com/atrupar/status…
Comme je prévoyais, il semble que l'ouverture d'une voie réservée covoiturage soit dangereuse pour les 2RM sur le périph parisien, pq les voitures qui s'y mettent sans avoir le droit se rabattent brutalement avant la caméra, sans contrôler → accidents. reddit.com/r/Motardie/com…
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Here is a graph of the function f being discussed in the particular case α=¼ (so that the fat Cantor set, aka Smith-Volterra-Cantor set, has Lebesgue measure ½). The question is: where is f differentiable? And are there points x where f′(x) exists but is neither 0 nor 1? pic.x.com/NAk9b3ic0d
Remarkably incisive and provocative question on MathOverflow: what is the set of points of differentiability of the “staircase” (cumulative measure function) for a fat Cantor set (obtained by removing the middle α part instead of the middle third)? mathoverflow.net/q/495986/17064
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It's very strange that, despite the central importance of the Killing form in the study of Lie algebras, the fact that it vanishes identically doesn't seem like an important or natural condition. (It just lies somewhere between “nilpotent” and “solvable”.)
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An explicit counterexample: ℂ³ with the Lie bracket [(t,x,y), (t′,x′,y′)] = (0, t·x′−x·t′, i·t·y′−i·y·t′) where i=√−1, that is, [e₀,e₁]=e₁, [e₀,e₂]=i·e₂ and [e₁,e₂]=0. Its Killing form vanishes, so it is solvable, but it is not nilpotent (it's a semidirect product).
I was today years old when I learned that a Lie algebra in characteristic 0 whose Killing form vanishes identically need not be nilpotent. (Although it is solvable by Cartan's criterion; and conversely, a nilpotent Lie algebra has zero Killing form.)
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@rdeolm1 … et même s'il y en avait, ils pourraient très bien juste céder le passage aux piétons qui ont le vert. Mais un débile a décidé qu'il fallait ça, et du coup les piétons qui ne connaissent pas attendent trois plombes, finissent par en avoir marre, et bloquent les voitures.
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@rdeolm1 … (Je sais que c'est ça la raison parce qu'il n'était pas comme ça avant, et on lui a donné ce comportement en même temps que le contresens cycliste a été marqué.) Évidemment, c'est complètement con, aucun cycliste ne profite jamais précisément de cet intervalle, …
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@rdeolm1 Il y a des raisons idiotes et d'autres très idiotes. Par exemple, un feu qui près de chez moi reste longtemps en 🔴 piéton + 🔴 voitures parce qu'il y a un contresens cycliste et que théoriquement des vélos devraient pouvoir passer. …
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@yiekshemash Comme ça ⬇️ par exemple? Ils m'ont répondu (en gros) «ça prendrait 5min par carrefour d'extraire l'info, et il y a 1500 carrefours régulés, votre demande n'est pas raisonnable». Abusé, mais je n'ai pas cherché à répliquer à leur refus ni à saisir la CADA. x.com/gro_tsen/statu…
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… Autre cas de figure: j'attends un peu plus longtemps, la voiture passe, et comme il n'y a plus personne, je passe juste après. Donc au 🔴 piétons, 🟢 voitures. Moins grave mais quand même toujours con: de facto, j'ai donc attendu le 🟢 voitures pour passer.
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… Résultat, l'automobiliste me déteste parce que je lui fais perdre encore plus de temps (voire, rater son feu 🟢, certains étant hyper courts. Mais POURQUOI on a des feux aussi cons? C'est presque fait exprès pour que les piétons apprennent à les ignorer! …
Je déteste cette situation: j'attends pour traverser une rue, le feu est 🔴 piétons, 🔴 voitures. Une voiture attend aussi. On attend TROIS PLOMBES comme des cons pour rien. Pile au moment où je decide que j'en ai vraiment trop marre et que je traverse, paf, 🟢 voitures. …
I asked a question on MathOverflow about the various conditions on geometric morphisms between topoi whose unit or coünit is monic / epic / iso. mathoverflow.net/q/495960/17064
@laurentbercot Can you confirm that I'm not misrepresenting your position in this reference to you on the other network?␤␤You can read the discussion without an account → bsky.app/profile/gro-ts… pic.x.com/A9XAZVWooW
RT @LYMFHSR: Après comment tu veux éviter que l'IA te rende stupide si même le BLOC-NOTES n'est pas à l'abri et que tu peux plus ouvrir un…
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@antoineducros Cf. cette entrée de mon blog, aussi: madore.org/~david/weblog/…
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@antoineducros Je ne peux pas installer France Identité sur mon téléphone, parce que j'ai installé une version d'Android sur laquelle j'ai un minimum de contrôle (je suis root), et ils estiment que c'est incompatible (et c'est un scandale). Cf. le fil finissant là: x.com/gro_tsen/statu…
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C'est marrant, aussi: les autorités 🇫🇷 font vraiment attention à ne vous donner le nouveau document d'identité que contre restitution de l'ancien pour destruction, alors que le 🇨🇦 propose «cochez la case si vous voulez qu'on vous rende l'ancien passeport aussi».
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Le passeport canadien a reçu un nouveau design, d'ailleurs, et pas juste parce que «au nom de Sa Majesté la Reine» a été remplacé par «au nom de Sa Majesté le Roi».␤␤(À gauche l'ancien, à droite le nouveau.) pic.x.com/dXOv8QVbou
Nouveaux papiers d'identité (enfin, plastiques d'identité, plutôt), fournis presque en même temps par deux pays.␤␤(Et j'ai pris un sacré coup de vieux sur la photo.) pic.x.com/mQJG9Amhwh
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@L3G33K @LaurentGarnier_ Ça c'est vraiment horrible comme truc. J'ai perdu plein de temps à Londres une fois à cause d'une rue numérotée de cette manière.
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@L3G33K @LaurentGarnier_ x.com/gro_tsen/statu…
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@_vila30 Je ne propose bien sûr pas de renuméroter les rues maintenant. Mais de le faire systématiquement pour toute nouvelle rue (encore mieux: utiliser la numérotation métrique, toujours).␤␤Mais pourquoi n'y a-t-on pas pensé avant? x.com/gro_tsen/statu…
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@Jilcaesel Certes, mais comment a-t-on réussi à ne pas penser à ça la dernière fois qu'on a fait une renumérotation des rues (vers 1805 pour Paris si j'ai bien suivi)? La découverte de l'infinité des entiers naturels, c'est pas exactement récent comme maths.
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@_vila30 Euh, c'est complètement évident, non? Je suis côté pair, je cherche le 123, je peux décider dans quel sens je dois aller et, en marchant, quand je vais décider de traverser, sans avoir à regarder les numéros de l'autre côté, souvent cachés ou peu lisibles de loin.
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@gine_robert Je suis bien d'accord, idéalement on devrait utiliser ça partout, tout le temps. Mais une numérotation non-métrique et quand même synchronisée entre les deux côtés, ça va, c'est raisonnable.
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@antoineducros Les nombres premiers, non, je ne défendrais pas trop ça. Par contre, utiliser les entiers ≡0, ≡1, ≡2 et ≡3 pour numéroter les deux côtés de la rue ET les deux sens, je pourrais bien défendre ça.
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@IanSolliec Il y a quand même plein plein d'endroits en 🇩🇪 où c'est le cas, de ce que je vois en essayant un peu au pif avec Google Street View. Je serais étonné qu'il n'y eût pas d'exceptions en 🇫🇷. (Sinon, je crois les exceptions fréquentes au 🇬🇧, j'en connais à Londres.)
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@bzavr Rassure-toi, il y a au moins deux exceptions à Paris aux «impairs côté gauche et pairs côté droit quand on fait face au sens croissant»: le chemin du Parc de Charonne dans le 20e, et la rue Simonet dans le 13e (je n'en connais pas d'autre).
Ce serait bien si les Français comprenaient que dans la numérotation d'une rue on peut synchroniser pairs et impairs en jetant quelques numéros par-ci par-là, et que c'est plus commode.␤␤Les entiers naturels ne sont pas une ressource rare, il n'est pas utile de les économiser.
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Of course the vertices of the hyperbolic triangle are hard to reach, especially the two ideal ones (having angle 0, so a Brownian motion has vanishingly small probability of landing near them).␤␤Riemann's conformal mapping theorem is just black magic!
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I added some plots of the conformal isomorphism found between the unit disk and the hyperbolic triangle in question, because it's interesting. The red and magenta curves are the image of circles of radii 0.99 and 0.999. pic.x.com/Oz4hENKMnw
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I wish someday I had the time to understand what ₂F₁ is all about, and why it's so important and why so many functions can be expressed in terms of it.
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The above defines the conformal mapping of the upper-half plane to the domain {x+i·y : x≥0, y≥0, (x−1)² + (y−1)² ≥ 1} (=the doubly ideal hyperbolic triangle with vertices at 0, 1 and i) taking 0, 1, ∞ to 0, 1 and i respectively.
Did I actually answer a MathOverflow question with a formula involving the ₂F₁ hypergeometric function, that I know nothing about? It would seem I did! (But actually, I basically just copied this from Wikipedia.) mathoverflow.net/a/495809/17064 pic.x.com/Jpc8GNtwZn
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… but I reiterate that those of us who hate both of them shouldn't rejoice because they're probably even more dangerous when fighting than when allied. x.com/gro_tsen/statu…
Six months was a bit longer than I expected the Trump-Musk bromance relationship to last (🧵🔽), and it's certainly fun to see them exchange niceties, … x.com/gro_tsen/statu…
RT @YourAnonCentral: pic.x.com/X6VmMvujzn
I asked a question on MathOverflow (and already got an answer!) about the relation to the effective topos RT(𝒦₁) of the corresponding realizability topos RT(𝒦₂^rec) on the computable part of Kleene's second algebra 𝒦₂. mathoverflow.net/q/495788/17064
RT @PoorOldRoloTony: DVDs don’t do that. BluRays don’t do that. Pirated files don’t do that. x.com/culturecrave/s…
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Also, their videos seem to be more about the motorcycle part than the faith part. But maybe the guy delivers a sermon halfway through the vlog, I didn't watch.␤␤(I expected this sort of things from the 🇺🇸 rather than the 🇬🇧, to be honest.) pic.x.com/j2cy0iXGzM
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(I'll settle for the “workout tips and Indo-European linguistics” or “Linux kernel development and early Byzantine history” channels if “étale cohomology and gay sex” isn't available, but “motorcycles and Christian faith” really doesn't cut it for me, sorry. 😁)
Another weird little corner of the Internet I stumbled upon: this YouTube channel that is about motorcycles but somehow also about the Christian faith.␤␤Nice of you to suggest this, YouTube, but I'll wait for a channel that's about étale cohomology and gay sex. pic.x.com/2br6xAEf5J
Wow. This was posted by the official account of the British embassy in China. x.com/ukinchina/stat…
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@laurentbercot A given country's economy can crash, so, yeah, if you want to store assets, don't store just one single currency.␤␤But if the entire world economy crashes, gold won't be worth anything either because it can't turn into bread: to prep for that, buy canned food.
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(Just to be clear, money is, fortunately, no longer primarily backed by gold. It's now mostly backed by loans that are at least related to the real economy, a far less absurd system. But lots of gold is still kept for historical reasons, e.g., ~1T€ are owned by the Eurosystem.)
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The absurdity of putting even part of our trust in money in the fact that some people store enormous amounts of one somewhat-useless-but-pretty chemical element and just do nothing with it, is absolutely fascinating.
I stumbled back on this video on gold by “Periodic Table of Videos” in which the professor was granted access to visit and film the bullion vaults of the Bank of England, and if you like gold bars, it's impressive and a bit surreal. youtube.com/watch?v=CTtf5s…
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@riontnafnel G20 de la Butte aux Cailles: google.com/maps/@48.82851…
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@ngspiensfr @laurentbercot J'ai commencé, mais après avoir implémenté les options --brand, --fruit, --sugar-amount, --organic et --cooking-method, j'ai abandonné.
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@laurentbercot Ah oui, parler de confitures sans jamais taper «configure» a été très très très difficile pour moi aussi.
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@laurentbercot … Donc in fine, ce n'est pas du tout à exclure qu'en prenant la version avec moins de sucre tu manges plus de confiture et plus de sucre au total. Tout ça est terriblement compliqué.
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@laurentbercot Mais sinon, pour info, minimiser la quantité de sucre ajouté dans la confiture n'est pas forcément un bon plan: d'une part ça se conservera moins lgtps, d'autre part, le fructose des fruits peut risquer de provoquer moins de sensation de satiété en sucre que le sucrose ajouté. …
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@laurentbercot … En fait, c'est «30% de sucre en moins» avec le fine print «qu'une confiture classique». (Par ailleurs, ils parlent aussi de cuisson au chaudron, donc la différence avec myrtilles cuites au chaudron est, euh… confuse. 🤔)
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@laurentbercot J'ai moi aussi plein de questions. Je ne voulais pas passer trois plombes à regarder les pots de confiture un par un, donc je n'ai pas la réponse à toutes les questions. Mais j'ai acheté la version «30% de sucre en moins», et il y a bien du sucre ajouté. …
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Donc là, si vous voulez de la confiture de myrtilles Lucien Georgelin, vous devez encore choisir entre: myrtilles, myrtilles cuites au chaudron, myrtilles bio, myrtilles −30% de sucre et myrtilles sans sucres ajoutés.␤␤(Quoi, y'a pas «myrtilles bio cuites au chaudron −30%»? 😆)
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C'est bien d'avoir le choix du fruit et de la marque, mais qu'il reste encore cinq confitures entre lesquelles choisir une fois ce choix effectué, c'est peut-être un petit peu too much, non? ted.com/talks/barry_sc…
Mon supermarché G20 de quartier, qui n'est pas grand du tout, propose le choix entre CINQ confitures différentes de myrtilles de la même marque (Lucien Georgelin). 🤯
Notez que j'ai vu un distingué astrophysicien (Brandon Carter pour ne pas le nommer) rappeler à ses filles et à moi que c'était EUX qui avaient marché sur la Lune, et pas NOUS.␤␤Il voulait dire: sa génération. x.com/gro_tsen/statu…
Il y a un mec cet après-midi à la salle de sport exactement comme Robert Webb dans ce sketch: il est habillé en merch du PSG de la tête aux pieds (alors que jamais avant) il vient de gloser sur la manière dont «on» «leur» avait mis 5–0 dans la gueule. x.com/gro_tsen/statu…
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I mean, one would tend to assume that Grok, being Twitter's official AI, and supposed to help avoid the spread of fake news, has access to the text of all tweets, and can't be fooled by a fake screenshot (let alone one whose context should clearly tell it that it's a joke).
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I say this because Grok, when asked to explain the thread, seems to think the screenshot is real, which is rather problematic (and also implies that Grok doesn't or can't read the alt-text of images). x.com/i/grok?convers… pic.x.com/HY9A3WTvCB
OK, sanity check: I hope it is 100% clear to all humans reading this (from the conditional “this would happen” and/or the “fake” word in the alt-text of the image) that the tweet in the image here is an humorous fake, and that Donald Trump did not, actually, post this. x.com/gro_tsen/statu…
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And then, of course, this would inevitably happen: pic.x.com/JHLbVcZt77
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Imagine that conversation?␤␤«␤“So, you can say I'm a brain surgeon. And you, Daniela, what do you do for a living?”␤␤“Me? Oh, I just work…” (puts on sunglasses) “…at the International Earth Rotation Service. As a matter of fact, I'm the Director or their Central Bureau.”␤»␤␤🤩
I still think Daniela Thaller has the BEST POSSIBLE JOB TITLE in the world. She is the “Director of the Central Bureau of the International Earth Rotation Service”.␤␤I am green with jealousy. x.com/gro_tsen/statu…
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@Moinsdeuxcat (Mais je prends note du fait que tu es un jeune rebelle très edgy.)
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@Moinsdeuxcat Je dirais que c'est un des plus faciles à commettre. Il fut une époque où écrire un programme pour lire des mp3 était probablement commettre cette infraction (moins la récidive, mais bon, il suffit d'en programmer deux 😁).
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@Moinsdeuxcat Parce que l'Administration a compris que les entiers naturels ne sont pas une ressource rare qu'il faudrait économiser. 👍␤␤(Sérieusement: parce que de temps en temps des infractions disparaissent, et on préfère que les codes soient stables dans le temps que de renuméroter.)
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Il y a certainement des jeunes rebelles très edgy qui jouent à «infraction-roulette»: tu tires un nombre représentant un NATINF valide, et tu dois commettre cette infraction, que ce soit le #5169 «meurtre» ou le #33749 «vente par un commerçant d'un cycle sans identification».
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Donc dans la même liste vous avez l'item #20295 («Crime contre l'Humanité: génocide») et l'item #22789 («Traversée irrégulière de la chaussée par un piéton») en passant par le #21279 («Exposition de biberon à tube», si, si, il y a une infraction juste pour ça).
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On se moque parfois des 613 mīṣvōt jewfaq.org/613_commandmen… des Juifs orthodoxes, mais apparemment en France il y a très précisément 16 832 choses qu'on n'a pas le droit de faire.
De temps en temps je repense au fichier NATINF justice.gouv.fr/documentation/… qui est la liste, aussi improbable et éclectique qu'un inventaire à la Prévert, de Tout Ce Qui Est Interdit en France. Il y en a (actuellement) exactement 16 832.
Ceci n'est pas un billet de blog. madore.org/~david/weblog/…
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@PSG_inside x.com/gro_tsen/statu…
Je crois que c'est le vraiment moment de reposter cette vidéo de Mitchell & Webb: youtube.com/watch?v=xN1WN0…
Worrying trend here on the evolution of the size of my blog posts over time. (Should I have used a log scale?) pic.x.com/RE4NLFLIoR
RT @tomgauld: My cartoon for this week’s @newscientist pic.x.com/0aegB3NOyX
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… And even the technical parts can be made at least somewhat palatable with some nice visuals. pic.x.com/c0vrMiIXI5
Joke aside, I think there's a good video documentary to be made about the CFSG. The non-technical part (the history of the subject) is interesting, there are many people to interview, and people like stories about records, so surely a ~15 000 page proof is impressive. … x.com/gro_tsen/statu…
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@vit_tucek As to seeing that (for finite groups) this definition coincides with the one given by the derived series, it shouldn't be too difficult (basically because the derived subgroup of a simple group G is trivial iff G is abelian, i.e., cyclic), but I don't have a reference at hand.
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@vit_tucek Basically you construct a tower of fields and at each step in the tower you have a cyclic group because you're taking a k-th root (cf. Kummer theory) so the Galois group of the entire tower is a composite extension of cyclic groups, which is my definition of “solvable”.
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… and with a surprise appearance by Anthony Hopkins as the quasithin case.␤␤(OK, this thread is 92 tweets long, which when discussing the CFSG seems very short, but even for me it's still long, so I think I'll stop here.) •92/92
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… I'm eagerly awaiting the TV series adaptation of the Classification of the Finite Simple Groups by Amazon Prime Video, starring Ian McKellen as Daniel Gorenstein, Edward Norton as Simon Norton, Timothée Chalamet as Richard Lyons, Mads Mikkelsen as the Monster Group … •91/92
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But after all this is still shorter than “Wheel of Time”, so whether there will eventually be a (3rd gen) machine-checkable proof of the CFSG remains to be seen, but for my part … •90/92
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So: the second gen proof is currently 4060 pages long, and (~30 years after it started), it seems that we've finished “theorem C₆ and theorem C₄*, case A” (whatever that may be). Good. There are probably roughly 2 or 3 more volumes to come before gen2 proof is complete. •89/92
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(To be completely clear, the above is the TABLE OF CONTENTS of the SKETCH of the STREAMLINED AND SIMPLIFIED (=2d gen) proof of the CFSG. Yeah.) •88/92
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The (already 165-page long!) volume 1 of the series gives an outline of how the proof is to proceed. (This, of course, assumes that you already know quite a bit about simple groups, it's by no means an introduction to the topic!) Its table of contents is interesting. •87/92 pic.x.com/bYsgTb1m0s
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Just to give a scale of the work: the latest (AFAICT) volume in this second generation proof is the 570-page volume 10 bookstore.ams.org/view?ProductCo… titled “The Classification of the Finite Simple Groups: Part V, Chapters 9–17: Theorem C₆ and Theorem C₄*, Case A.” •86/92
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This “second generation” proof is being published by the American Math Society as a series of volumes written (mostly) by Daniel Gorenstein (now deceased), Richard Lyons and Ronald Solomon. This rewriting has been going on for… 31 years now. 😵 •85/92
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But still, an effort is underway to at least rewrite, streamline and simplify the proof of the CFSG and publish it as a series of books that can be read more easily than hundreds of papers scattered across multiple journals over more than two decades. •84/92
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… as part of a team effort spearheaded by Georges Gonthier which concluded in 2012, so we can now say with 100% confidence that this part of the proof is entirely correct. So far, formalizing the entire proof of the CFSG in a proof checker seems too difficult. •83/92
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For example, the “Feit-Thompson theorem”, which asserts that every finite simple group apart from the Z_p has an even order (number of elements), which is the very start of the CFSG, and already a long and arduous theorem, was formalized in the Coq proof checker, … •82/92
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The ideal thing would be to formalize the proof in a computerized proof checkers. This has been done for other long and difficult theorems before (and tiny errors are always found in the proofs, though they are almost always easy to fix and don't compromise the result). •81/92
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… so even if specialists “were sure that” they could complete it, this was only really written and published in 2004, so it's only then that the proof can really be claimed to be fully complete. But how sure are we that other gaps haven't gone unnoticed? •80/92
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Of course, such an enormously complicated proof (which, at its heart, is a very fastidious enumeration of cases, subcases and sub-subcases) is bound to have errors in it. In fact, an entire part was missing, the “quasithin” case, from the original proof, … •79/92
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… Robert Griess, who proved the existence of the hitherto elusive “Monster”, and the one whom we could describe as the conductor of this orchestra of group theorists, Daniel Gorenstein, who eventually announced that the proof was complete.) •78/92
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(Of course, some names stand out more: like J. H. Conway who not only discovered three sporadic groups but also co-authored the ATLAS, a book which deserves its own story; Bernd Fischer and Zvonimir Janko who also discovered several sporadics each, … •77/92
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This is, of course, a reminder that mathematics is a collective accomplishment: there was no single mastermind, no solitary genius behind this monumental achievement that is the CFSG: dozens if not hundreds of group theorists each brought their brick to the wall. •76/92
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… and it was only near the end that people could look back and say “oh, if we collect this big list of papers and put them together, we can summarize what was proved by this monumental theorem that classifies all finite simple groups”. •75/92
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Of course, this first generation proof was done “in the blind” because the first authors had no idea what they were trying to prove, they were discovering sporadic groups as they were filling in the cases of an attempt at classifying finite simple groups, … •74/92
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The original (or “first generation”) proof is estimated to span roughly 15 000 pages of mathematical papers by maybe 100 authors, from roughly 1960 to roughly 1985 (it really depends on what you count as being part of the proof or merely referenced by it). •73/92
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It took me 71 tweets merely to scratch the surface of what this theorem even is about, this is very far from stating it, and the proof is… well, the proof is arguably the longest and most complicated mathematical proof ever written by human beings. •72/92
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The CFSG is enormously more complicated. Already the statement of the theorem is very difficult to give: merely to state it, we need to define all 18 families and 26/27 exceptions (and also exceptional isomorphisms inside the list that I didn't talk about). •71/92
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So we can view it as a kind of monster version of the Killing-Cartan classification of simple Lie groups that I discussed above: this one had 4 infinite families + 5 exceptions, and was already a major achievement of 19th century math. •70/92
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This, essentially, is the statement of the Classification of Finite Simple Groups (CFSG): that the list of 18 families + 26 exceptions is the full list of all finite simple groups (these exist, and there are no others: it's not like we just haven't found more). •69/92
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… ²A_n, ²D_n, ³D₄, ²E₆, ²B₂, ²F₄ and ²G₂) but this is a bit misleading because some are double families and others are single families. Anyway. Apart from these, there are 26 (or 27) exceptions, known as the “sporadics”, the largest of which is the “Monster”. •68/92
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… and the “groups of Lie type” (themselves further divided into Chevalley groups and twisted groups, and into “classical” and “exceptional” families); altogether, we generally say there are 18 infinite families (Z_p, 𝔄_n, A_n, B_n, C_n, D_n, G₂, F₄, E₆, E₇, E₈, … |•67/92
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‣✨The story so far:✨ in trying to understand all possible forms of finite symmetries we are led to try to classify their “atoms”, the finite simple groups. Some of these fall into infinite families: the cyclic groups Z_p, the alternating groups 𝔄_n, … •66/92
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And then there are 6 more sporadics that don't even fit that pattern of the “happy family”: they are known as the “pariahs”, the largest of which (smaller than the Monster, but not living inside it) is the Janko group J₄ with 86 775 571 046 077 562 880 elements. •65/92
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To be clear, we can ✱prove✱ that these groups and patterns between them exist, but at some level we really don't “understand” what this is all about. Why are these groups out there? What's this business with three generations and the number 24? Why does it stop here? •64/92
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… eight further sporadic groups including the Monster, “Baby Monster” and the Fischer groups. Each generation of the “happy family” of sporadics is a kind of elaboration of the previous generation, and the number 24 plays a role at every turn. •63/92
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… so basically they act on 24 objects; the “second generation” consists of (seven further) sporadics groups that “live inside” the Conway group Co₁, which acts on an object in 24 dimensions (the “Leech lattice”); and the “third generation” are … •62/92
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… and the 20 sporadics that “live inside” the Monster (sometimes known as the “happy family”) are themselves sometimes divided into three “generations”: the five Mathieu groups (which all live inside M₂₄) are the “first generation” of the “happy family”, … •61/92
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Even within the sporadics, there seems to be a sort of pattern: 20 of the 26 sporadic groups, including the Monster itself, “live inside” the Monster group (technically, they are subquotients of it), so the Monster encompassess most — but not all — of these sporadics; … •60/92
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… was finally proven by Robert Griess in 1982. Even then, we can't say that we really understand “why” the Monster exists, why this bizarre and exceptional form of symmetry is “out there”, acting on a 196 883-dimensional object. See youtube.com/watch?v=jsSeoG… for more. •59/92
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… first, its existence was conjectured by the fact that it left a kind of set of footprints (what is known as a “character table”) that we could detect and that suggested the existence of such a group in the 1970's, and it was only in 1982 that its existence … •58/92
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This “Monster group” is one of these mysterious mathematical objects which really make it hard to argue that mathematics is anything other than discovered: nobody decided to invent this thing, it just popped up out of our attempts at classifying symmetries: … •57/92
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The smallest of these 26 sporadics is the Mathieu group M₁₁ (7920 elements) mentioned above. The largest is the “[Fischer-Griess] Monster group” with 808 017 424 794 512 875 886 459 904 961 710 757 005 754 368 000 000 000 ≈ 8.1×10⁵³ elements. •56/92
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(Some ppl say there are 27 sporadics: this depends on what you count as a sporadic, because there is a group called the “Tits group” ²F₄(2)′ of order 17 971 200 that is not exactly a (twisted) Lie type group but “one half” of one (²F₄(2)), so you can count it or not.) •55/92
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During the 1960's and 1970's, mathematicians started looking for other finite simple groups that, like the Mathieu groups, didn't belong to any one of the known infinite families: these came to be known as the “sporadics”. Eventually, 26 of these would be discovered. •54/92
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So at this stage we have several infinite families of finite simple groups (some people say 18 families, but it really depends how you count) and five strange outliers, the Mathieu groups, that don't seem to belong to any infinite family. •53/92
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(If you want to play with them, I once wrote a little JS page madore.org/~david/misc/m2… that lets you play with M₂₄ (and M₁₂). You can try to scramble the puzzle using the ‘¿’ button and then use the commands above to unscramble it… if you can figure out what they do.) •52/92
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The Mathieu groups M₁₂ and M₂₄ have 95 040 and 244 823 040 elements respectively, and M₁₁, M₂₂ and M₂₃ are smaller (M₁₁ with 7920 is the smallest of what would become known as the “sporadics”). •51/92
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Yes! In fact, such groups had been known since the 1870's: Émile Mathieu had discovered bizarre groups of symmetries on 12 or 24 objects (with subgroups on 11, 22 and 23 objects) that were simple and did not belong to any of these families. •50/92
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So, in the early 1960's, the following finite simple groups were known: the cyclic groups Z_p, the alternating groups 𝔄_n, and the “groups of Lie type” (Chevalley or twisted) derived from the Killing-Cartan classification of Lie groups. Are there others? •49/92
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Soon after Chevalley, in 1959, Robert Steinberg discovered a modification of Chevalley's construction that gave even more infinite families (³D₄, ²E₆, ²A_n and others: “twisted groups”). Without getting into details, these are collectively known as “groups of Lie type”. •48/92
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Note that these groups can be quite large: already E₈(2) (smallest of the E₈ family) has 337 804 753 143 634 806 261 388 190 614 085 595 079 991 692 242 467 651 576 160 959 909 068 800 000 ≈ 3.4×10⁷⁴ elements (more than the “Monster” below). •47/92
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So each of A_n, B_n, C_n and D_n now gives rise to a “double family” of finite simple groups because we have two parameters (n and q) that we can vary. And each of “exceptional” Lie groups G₂, F₄, E₆, E₇ and E₈ gives rise to a whole family of finite simple groups. •46/92
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… for each one of the groups of the Killing-Cartan classification (A_n, B_n, C_n, D_n, G₂, F₄, E₆, E₇ and E₈) and if q is the power of a prime number, with a small number of exceptions (that aren't simple), we get a finite simple group from Chevalley's construction. •45/92
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… (at least if n≥3 or q≥4), which we denote “PSL(n,q)”, and this is what the Chevalley construction gives you when you apply it to the A_n (well, A_{n−1}) family of the Killing-Cartan classification. To summarize: … •44/92
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… and if you do this, you generally (=with finitely many exceptions) get a finite simple group. For example, if you know what this means, the n×n matrices with determinant 1 over a field with q elements, up to multiplication by a scalar, gives us a finite simple group … •43/92
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To be just a little less vague for those who know what this means: the simple Lie groups of Killing and Cartan involve a “field”, generally that of real (ℝ) complex numbers (ℂ), and Chevalley described a way to replace them by finite fields (also due to Galois!): … •42/92
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A whole bunch of finite simple groups were described in the 1950's (some were know before that) by Claude Chevalley using the following brilliant idea: we can take the simple Lie groups of the Killing-Cartan classification and make simple groups out of them. •41/92
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So, so far, I described two kinds of “atoms of finite symmetry” or finite simple groups: the cyclic groups Z_p (with p prime) and the alternating groups 𝔄_n (for n≥5). What are the others? Here's where it gets pretty complicated. •40/92
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… 𝔄_n, consists of merely the “even” permutations, or “alternating group”. (This is familiar, for example, from the “15-puzzle” or “taquin”: the possible permutations of the 15 squares which put the hole back in its place are the group 𝔄₁₅ of even permutations.) •39/92
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If we consider all manners of permuting n objects, this forms a group known as the “symmetric group” 𝔖_n, and it turns out that, at least for n≥5, this group has two atoms in its chemical formula: one is Z₂ that I already mentioned, and the other … •38/92
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Aside from these very easy cyclic groups Z_k, we have another kind of finite simple groups (atoms of symmetry) that's not too hard to describe: the “alternating groups” 𝔄_n: these are related to the permutations of n objects. •37/92
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(As a side note: the terminology “simple” — for the atoms — is really annoying because I keep wanting to say that something is simple in the sense of being easy, and certainly solvable groups are the easiest. But “simple” is taken as a technical term. Ah well.) •36/92
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(For example, the abelian groups, namely those in which composition is commutative: performing symmetry g₁ then g₂ is the same as g₂ then g₁, are necessarily solvable. These finite groups are very easy to classify.) •35/92
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Finite groups whose “chemical formula” involve only these “cyclic” atoms Z₂, Z₃, Z₅, Z₇, etc., are said to be “solvable”. This terminology comes from Galois's groundbreaking insight that these are the ones which appear in solving equations using n-th roots. •34/92
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Technical note: actually, the Z_k are simple only when k itself is a prime number, because if k = m·n then Z_k can be “broken up” into Z_m and Z_n. So we have the atoms: Z₂, Z₃, Z₅, Z₇, etc., which are the most basic forms of symmetry (cyclic symmetry). •33/92
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… This is really the most basic form of symmetry possible, and I think it's familiar to anyone even when we don't know the technical terms (think of rotating a knob that has k possible positions, equally spaced: this wouldn't make for a very fun puzzle!). •32/92
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So, back to our main story: what are these possible “atoms of finite symmetry” (finite simple groups)? Some aren't too complicated to describe: notably, Z_k, known as the “cyclic group of order k”, is the group of rotations of a regular k-gon. … •31/92
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… but that this 𝔄_n atom cannot appear as part of the symmetries of an expression built using k-th roots (only “Z_k” atoms can occur here). So Galois initiated the study, not just of symmetries of algebraic equations (“Galois theory”) but of finite groups themselves. •30/92
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He showed that the symmetries of general algebraic equation of degree n contain an “atom of symmetry” [← Galois wouldn't have used this language, nor is it common mathematical parlance: the modern technical term is a “Jordan-Hölder factor”] “𝔄_n”, … •29/92
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… he considered the symmetries of the equation (essentially, the ways you can permute its solutions so as to leave all relations we can write between them unchanged), something we now call the “Galois group”, and compared it to the symmetries we can get using k-th roots. •28/92
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… until Abel and Galois proved that no such general formula exists — it's not that higher degree equations can't be solved, but they can't be solved by the operation of taking n-th roots). ❧ Galois's approach is beautiful and opened entire new fields of mathematics: … •27/92
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… x = (−b±√(b²−4a·c))/(2a) expressed using the square root √ operation; similar formulas with cube and 4th roots for degrees 3 & 4 were found in the 16th century by the likes of Cardano, Tartaglia and Ferrari but the general degree 5 equation remained “unsolved”, … •26/92
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… Galois was interested in proving that algebraic equations of degree 5 or more can't be “solved in radicals” unlike those of degrees 2, 3 and 4, meaning you can't write their solutions with k-th roots (in degree 2 the equation a·x² + b·x + c = 0 has solutions … •25/92
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Some of these “atoms of finite symmetries” had been known for a long time: Évariste Galois (building on earlier work of Adrien-Marie Legendre) had started the study of finite groups (and groups in general) around 1830: … •24/92
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… is a start toward the mathematical description of the Rubik's cube. ❧ Anyway, just like in the 1890's the possible simple parts of Lie groups were fully classified by Killing and Cartan, the issue later arose to find, describe and classify all finite simple groups. •23/92
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… because you still need to understand how pieces “fit together”, and what makes the Rubik's cube puzzle puzzling is that you don't get to act on the parts independently. But still, this “empirical chemical formula” of “one 𝔄₈, one 𝔄₁₂, seven Z₃ and twelve Z₂”, … •22/92
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For example, the Rubik cube's group's simple parts are 𝔄₈ (essentially, permutations of the vertices), 𝔄₁₂ (essentially, pns of edges), 7 copies of Z₃ (rotating the vertices) and 12 copies of Z₂ (mostly flipping the edges). This alone doesn't solve the puzzle: … •21/92
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Now classifying all the possible parts, viꝫ. simple groups, doesn't mean that we fully understand all groups (forms of symmetry), just like knowing all chemical elements doesn't mean we understand all of chemistry, but it still gives us a good and necessary first step. •20/92
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(For those who know what this means: a simple group is one that has no normal non-trivial subgroup. Otherwise, if H is a normal subgroup of G, the simple parts [proper term is “Jordan-Hölder factors”] of G are those of H together with those of G/H, recursively.) •19/92
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The groups which can't be broken up into smaller groups are called “simple” groups (this is a technical term: it doesn't mean that they're simpler to understand). Metaphorically we might say that groups are molecules of symmetry and the simple ones are symmetry “atoms”. •18/92
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I won't try to explain what “made up” means, but very very roughly you can “break” certain groups into parts and somewhat understand them by understanding the parts. (Like the Rubik's cube puzzle can be understood by the movements of the edges and of the vertices.) •17/92
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I said earlier that classifying all groups is hopeless. So we restrict ourselves to a particular kind of groups, such as finite groups, or Lie groups. But even that is too hard. However, it turns out that groups are made up of other groups. •16/92
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Anyway, the reason I mention this Killing-Cartan classification theorem in relation to the CFSG is twofold: first, it is a kind of “junior version” of the CFSG (Lie groups are ✻much✻ easier to classify than finite ones); second, it is used by it. But back to the story. •15/92
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But the five exceptional groups G₂, F₄, E₆, E₇ and E₈ where a genuinely new discovery by the classification effort, and turned out to be connected with many “exceptional” mathematical objects such as the octonions (G₂ is essentially the symmetries of the octonions). •14/92
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The four infinite families (known as “classical” Lie groups) were known before Killing and Cartan: B_n and D_n, for example, are the groups of symmetries of the sphere in odd and even dimensions (there are reasons to separate these), also denoted as SO_{2n+1} and SO_{2n}. •13/92
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In its simplest variant (for the “compact” Lie groups — a kind of finiteness condition), it tells us that simple Lie groups come in four infinite families (A_n, B_n, C_n and D_n) plus five “exceptional” groups (G₂, F₄, E₆, E₇ and E₈). •12/92
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This Killing-Cartan classification is one of the crown jewels of 19th century mathematics. (It was later simplified by others, including Eugene Dynkin.) It gives us a grasp on all possible “continuous” forms of symmetry. •11/92
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Lie groups were introduced by Sophus Lie and Friedrich Engel (not to be confused with Friedrich Engels! 😅) in the 1880's, and in the 1890's, Wilhelm Killing and Élie Cartan completed the classification of simple Lie groups (I'll explain the term “simple” shortly). •10/92
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I won't try to explain what a Lie group is (and there are various flavors), but very very (very) roughly, it's a form of continuous symmetry that an object can have. They are hugely important in theoretical physics (physical concepts generally have such “Lie” symmetries). •9/92
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Some forms of symmetries, rather than finite, are continuous: if you take a sphere, for example, you can't just move it around in 24 different ways like a cube, but in a continuous manner. These also form a group (“SO₃”) but not a finite one: it's called a “Lie group”. •8/92
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Here's one thing we can do to restrict the problem: look at specific kinds of groups. The one that the CFSG is about are finite groups, so: objects that have only finitely many symmetries (like the Rubik's cube). But let me first say a word about another kind. •7/92
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So it would be nice to understand them better and to get a grasp of the various kinds of groups that exist, or, as we say in mathematics, to “classify” them: to understand all possible forms of symmetry. But if we don't restrict the problem further, it is utterly hopeless. •6/92
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Anyway, symmetries and, consequently, groups, are ubiquitous in mathematics, but also in theoretical physics (e.g., they play an essential role in defining conservation laws and building up the “gauge fields” of the standard model of particle physics), cryptography, etc. •5/92
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… but they can be a little more combinatorial: for example, the “Rubik's cube” puzzle, which many people are familiar with, is basically about exploring a group with 43 252 003 274 489 856 000 elements (the mechanically available transformations of the puzzle). •4/92
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Most people are at least aware of geometrical symmetries: “in what ways can you rotate a cube by keeping its overall position fixed?” (e.g., rotate by 90° around a face, or 120° around a diagonal) is an example of a (finite) group (here with 24 elements or “order 24”), … •3/92
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So, I'm not going to define what a “group” is formally (see youtube.com/watch?v=mH0oCD… for an attempt at an explanation), but I like to describe it informally as “a form of abstract symmetry” that an object (mathematical or otherwise) can have. •2/92
Probably one of the most monumental achievements of human mathematics is the Classification of Finite Simple Groups (“CFSG”), a proof whose current incarnation is about 15 000 pages long spread across many articles by different authors. What is this all about? 🧵⤵️ •1/92
That feeling when you've just spent an hour of computer time (mostly disk thrashing time, so making the box nearly unusable) to recompile a new Firefox version, and realize at the end that you checked out the wrong commit and just rebuilt the version you were already running. 😣
RT @JacqBens: @gro_tsen I forget what newspaper, following weekend negotiations that ended a New York subway workers' strike, published the…
Ah, well… Sic transit gloria wednesdi.
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@laurentbercot And yes, he is pretty cute. I mean, Aragorn is the one I'd bang, but Sam is the one I'd much rather cuddle with.
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@laurentbercot I forgot where I read the remark that true love is when you look at someone with the same adoring eyes that Sam keeps looking at Frodo in this trilogy. 😍
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Of course, now that I've solved it, I think the question was absolutely trivial (in the sense that it is a trivial consequence of standard facts in descriptive set theory around analytic sets). 🤷 x.com/gro_tsen/statu…
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And now I'm super happy to have solved this question that had been bugging me all week: the image of a lower semicontinuous function [0,1]→ℝ is analytic but it can fail to be Borel. mathoverflow.net/a/495324/17064
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I love how Grok tries to gaslight me by explaining that a term it asserts was coined in 1943 «predates» Kafka's 1915 parable. (But it may still be right that there is little connection, of course.) x.com/i/grok/share/w… pic.x.com/tnk7QATbrp
Did the English word “gatekeeping” appear as a reference to Franz Kafka's famous parable ‘Before the Law’ (which is about a man faced with a literal gate-keeper¹ of the Law)?␤␤1. “Türhüter” in German. (OK, this means “door-keper”: “gate-keeper” would rather be “Torhüter”.)
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This one is pretty funny as well, for different reasons: mathoverflow.net/q/495228/17064␤␤(Also for the fact that it claims to be inspired by season 5 episode 14 of ‘The Flash’.) pic.x.com/mt6rBPm3rt
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@laurentbercot Narrator: “And this is the story of how Laurent became a creature of the night, wandering the streets of Metropolis and asking ‘What is the airspeed velocity of an unladen swallow?’ to unsuspecting passers-by.”
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Plot twist is that, 100 years later, people discover that the Education Vigilante never existed, it was just a legend that a certain Hari Seldon created and got people to believe in. But by the time people realize this, it's already too late.
Existential Comics may have a dangerously good point about what it takes to solve many of our society's problems, there. existentialcomics.com/comic/604␤␤(Incidentally, ✳︎who✳︎ said citizens must be “forced to be free”? <looks it up> Oh, Rousseau, of course. I totally knew that. 😅)
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@antoineducros Ah oui, «genre»! Comment ne pas se réjouir que la terminologie de la géométrie algébrique entre passe dans le langage courant? 😏
A moment of self-doubt dread… fortunately soon overcome. poorlydrawnlines.com/comic/not-amaz… pic.x.com/n6Dyz1qgfv
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Snapshot of former version at the Internet Archive: web.archive.org/web/2025042001…
The Vatican's Web site: left, on 2025-04-20; right: today.␤␤Clearly the younger pope has embraced Web 2.0 as canon. pic.x.com/NCyfFoeVu9
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(Pas le moindre début de commencement d'argument dans ces articles pour expliquer en quoi cette locution serait «fautive» ou critiquable, d'ailleurs.)
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Évidemment, on peut compter sur les prescriptivistes réacs du Figaro et de l'Académie française pour prétendre que cet usage est «fautif» (whatever that may mean): lefigaro.fr/langue-francai… et academie-francaise.fr/en-mode
Quand est-ce que la locution «en mode <qqch>», maintenant très courante en français familier¹ est apparue, et a-t-on des informations sur l'origine de sa popularité? (Ça vient de l'informatique?)␤␤1. Du genre «j'y suis allé en mode j'm'en fous» ou «j'étais en mode véner».
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So, if you need to know what a triangle is: pic.x.com/jZdjut8p9l
The title of this research math question on MathOverflow is excellent. mathoverflow.net/q/257495/17064 pic.x.com/c5j6CwA9JD
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⚠️ Ne pas confondre le parc départemental des Hautes Bruyères avec l'arboretum des Grandes Bruyères, qui est beaucoup beaucoup plus beau, mais aussi plus difficile d'accès. x.com/gro_tsen/statu…
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… L'arrêt de métro lui-même mérite un coup d'œil par la profondeur de son puits, d'ailleurs. pic.x.com/4a0vWeuv2C
Bon à savoir: l'arrêt «Villejuif–Gustave Roussy» (récemment ouvert) de la ligne 14 du metro parisien communique directement avec le parc départemental des Hautes Bruyères, fournissant un accès commode à celui-ci, qui est plutôt agréable. …
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Réponse fournie sur l'autre réseau: «apparemment ça correspondrait à une division en postes de police seniorsreporters.bordeaux.fr/2025/02/18/a-l… et peroliv.blogspot.com/2022/12/arrond… Y a des références aussi sur Gallica au justice de paix de ces arrondissements.»
Il y a à Bordeaux en certains endroits de mystérieuses plaques portant un (ancien?) numéro d'arrondissement. Par exemple ici (place Mitchell: «2e Arr^t»): google.com/maps/@44.85054…␤␤Quelqu'un sait-il à quoi ça correspond(ait)? pic.x.com/HOvQ7AGlxe
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Réponse sur l'autre réseau: on me signale que c'est une limite de cantons (un canton peut être plus petit qu'une commune). fr.wikipedia.org/wiki/Cr%C3%A9t…
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Y a-t-il des subdivisions administratives plus petites que la commune, en France?
Pourquoi est-ce que sur la carte des limites administratives sur Géoportail la commune de Créteil semble divisée en deux par une ligne grosso modo nord-sud? À quelle limite correspond-elle? geoportail.gouv.fr/carte?c=2.4570… (Je parle de celle verticale à peu près au milieu de mon image.) pic.x.com/QEC9c0k4yB
I answered a question on MathOverflow by explaining (though this may not have been what the question was about 😐) why the sequence that counts the number of reduced words of length n in a Coxeter group has a rational generating function. mathoverflow.net/a/495077/17064
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Update: it's possible to add a custom search engine by adding the (hidden! 😤) `browser.urlbar.update2.engineAliasRefresh` preference to true, then going to about:preferences#search and clicking on “Add” below the “Search Shorcuts” list.␤␤Why hide it like that? WTF, Mozilla? 🤦
I'll probably post details later, but it seems infuriatingly difficult to persuade Firefox (desktop edition) to add a user-specified URL as a custom search engine to the browser, without installing Yet Another F😖cking Extension for this.␤␤If you know a simple way, please tell!
RT @pbeyssac: Inutile de dire que si Microsoft est obligé de fermer le compte sur injonction de Trump, l'accès à tout son contenu était a f…
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I see this on ① Twitter on PC, ② Twitter on Android, ③ Bluesky on PC, ④ Bluesky on Android. Nothing makes any sense whatsoever. (PC running Debian Linux and Firefox 138.0.4. Android running some version of LineageOS.) pic.x.com/sJHu2K9Nfx
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@JacqBens That's also how I say it. So it took me a long time to understand why so many people were joking about a pun that I couldn't understand. But I imagine our pronunciation must be less frequent (otherwise the pun wouldn't be so widespread).
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A test:␤␤⁃ Default style: “☠✨⬆🌕🐿👁👍” and “🐧”␤⁃ Explicit emoji style: “☠️✨️⬆️🌕️🐿️👁️👍️” and nonstandard “🐧️”␤⁃ Explicit text style: “☠︎✨︎⬆︎🌕︎🐿︎👁︎👍︎” and nonstandard “🐧︎”
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@JacqBens (Maybe because in “j'ai pété” the stress would be more heavily on the last two syllables and there's a micro-pause before it, whereas in “GPT” it's more uniform. I'm not sure.)␤␤But it's a bit like asking how to say the planet ♅ in English without middle schoolers giggling. 😅
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@JacqBens The “Chat” part seems almost always pronounced as in English. The “GPT” part is pronounced by reading the letters as in English or (more often) as in French. In the latter case, I think it's a matter of overall intonation which makes it sound like “GPT” and not “j'ai pété”.
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The link to the list of emoji variation sequences is: unicode.org/Public/UCD/lat…
I asked a question on Reddit /r/Unicode about the logic behind the list of Unicode characters that have both a text style and an emoji style. reddit.com/r/Unicode/comm… pic.x.com/f6adXsMJvC
Another “shit, I never thought about this question and I realize I know nothing about it” moment: is the image of a lower semicontinuous f:[0,1]→ℝ a Borel set? mathoverflow.net/q/494998/17064
Embarrassing situation on MathOverflow where, in answer to the same question, we have a proof that alternative division algebras in characteristic 2 are associative, and a counterexample showing that they aren't. So, who's wrong? mathoverflow.net/q/485668/17064
I almost missed that today is the 150th anniversary of the signing of the Metre Convention! en.wikipedia.org/wiki/Metre_Con…
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@JacqBens You have the causality the wrong way: French mathematics does not cause hunger for power, it attracts the power hungry, because everybody knows¹ mathematicians secretly rule the world, and of course we do it in French.␤␤1. (Everyone who read Asimov's ‘Foundation’ books, that is.)
Ce type est le descendant direct de: Pierre Curie, Marie Skłodowska-Curie, Irène Joliot-Curie, Frédéric Joliot, Paul Langevin, Michel Langevin et Hélène Langevin-Joliot. La pression pour devenir un physicien brillant devait être… forte. 😆 fr.wikipedia.org/wiki/Yves_Lang…
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@JacqBens … But the added twist with Touadéra is that he chooses to keep teaching mathematics while being president: notrevoix.info/info/articles/…
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@JacqBens Someone also pointed out to me on the Other Place that Faustin-Archange Touadéra, the current President (and former Prime Minister) of the Central African Republic also has a math doctorate and some publications in partial differential equations: ⬇️ pic.x.com/2CQXLETyNL
RT @WereInHellYT: The collected art and knowledge that humans have produced throughout the ages is all of our birthright and these tech gho… x.com/hsrdirector/st…
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@CarloDallapicc1 ⓐ I agree that the issue of “free will” is a red herring, but I'm not the one who chose to use that term.␤␤ⓑ Exactly. So the point is that while the laws of physics can influence the experimenters' choices, they can't influence mathematical constants: hence the experiment.
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@ArthurB Yes, I think it's more crazy. Because the behavior of the experimenter ✺is✺ unquestionably an effect of the laws of physics. The decimals of π, most people will agree, are not.
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… experiment where the choices of measurement are done following a purely mathematical rule like the decimals of π (in base 3). These are deterministic, but effectively random, and it would be crazy to suggest that the laws of physics “know” what rule you're following. •3/3
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… we can just say that the laws of nature predict both the experimenter's choices of measurement and the outcome of measurement, and Bell's theorem says nothing. ❧ But I believe we could to some extent test (and refute?) this explanation as follows: repeat a Bell-type … •2/3
Several people (including @skdh) have proposed resolving the contradiction between Bell's inequalities and local realism (hidden variable) interpretations of Quantum Mechanics by appealing to superdeterminism: namely, if the experimenters don't have free will, … •1/3
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@JacqBens The new Romanian president-elect has more than just a background: theses.fr/1998PA132019 (also, he went to the same École normale supérieure that I went to, a few years before me).
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@antoineducros Ce n'est pas exactement grave, mais ça m'arrive de vouloir faire référence à quelque chose qui se produit de manière à peu près régulière, fût-elle rare, et il me faut un mot pour ça (sans me lancer dans des explications de matheux).
Ça m'agace que «régulièrement» soir utilisé comme signifiant (en gros) «assez fréquemment». Un évènement peut se produire régulièrement mais très très rarement: qqch qui arrive systématiquement une fois tous les milliards d'années est régulier mais extrêmement rare.
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@laurentbercot Specifically, I've never encountered ANYONE other than myself, who's not a Firefox dev or distro maintainer (or equivalent), and who compiles their own Firefox. So of course they have little motivation to make it “newbie-friendly”.
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@laurentbercot I also suspect that a big part of the enshittification comes from the fact that almost nobody compiles anything anymore: only the project devs themselves, or distro maintainers (who use their own flavoring). Many projects have become almost impossibly complex to build.
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(In the case of Firefox, that nonsense is called “mach”, and it's a f👿cking abomination. It used to be the case that one could type “make” after the configure step, but no more: one must now go through this awful gate.)
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There used to be a nice Unix tool called “make” which would only recompile stuff that actually needs to be recompiled. It appears that modern projects either have forgotten how to use it, or misuse it as a kludge to just recompile everything, or wrap it in their own nonsense.
Presently compiling Firefox 138.0.4, because it appears that it contains the fix for an important security issue. I'm doing this in the built tree of a previous 138.0.1 compilation. Only very few files have been changed. So, WHY IS IT RECOMPILING EVERYTHING? 🤬
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@RomainCGP «Déjà été, pas ouf»? C'est un peu court, jeune homme!␤On pouvait dire… Oh! Dieu! … bien des choses en somme…␤En variant le ton, — par exemple, tenez:␤Dégoûté: «Ce caviar, il puait à plein nez.»␤Fâché: «Michelin lui donna 3 étoiles,␤Je l'aurais renvoyé à ses malheureux poêles.»
RT @weirddalle: pic.x.com/mpv7cl1ihK
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… je n'irais pas jusqu'à dire que c'était «2× meilleur» (ni moins 3×), donc je pense qu'en matière de rapport qualité/prix, on n'est pas à l'optimum pour ce qui me concerne. Peut-être que je suis trop rustre pour apprécier à sa juste valeur une telle sophistication! 😅 •20/20
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Pour l'expérience, pour essayer au moins une fois, je dirais que ça les vaut. Ceci étant, c'est ~2× le prix d'un restaurant avec «seulement» une ✻ au Michelin (cf. x.com/gro_tsen/statu… ), et s'il me semble que ce ✻✻✻ était effectivement encore meilleur, … •19/20
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L'addition était, évidemment, assez salée: 724€ pour deux (apéritif, menu, eau et cafés); et c'est parce que nous ne buvons pas d'alcool. (Nous étions d'ailleurs loin d'être les seuls dans ce cas, j'ai remarqué.) •18/20
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Même le pain était extra, ou encore le «pré-dessert» (une glace à l'aneth, si je me rappelle bien, pour faire la transition entre le salé et le sucré), ou jusqu'à la petite truffe au cacao accompagnant le café. •17/20
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… tout était délicieux. Je ne savais pas que des petits pois pouvaient être aussi bons; le poussinet a adoré le soufflé à la crème de comté; et la tarte au cacao amer accompagnée de glace à la fleur de lait et vanille de Madagascar était aussi bonne qu'on le pense. 😋 •16/20
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Tous les plats (y compris les amuse-bouche et le «pré-dessert») étaient absolument exquis. Ce que j'ai préféré, était l'«asperge blanche, escabèche au miso blanc, poutargue et zestes de citron jaune» et le dessert nº1 (crumble de pollen et glace au miel), mais vraiment … •15/20
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Les quantités étaient aussi très bien dosées. Je craignais de ressortir avec l'impression de devoir exploser, mais non. Mais je ne suis certainement pas parti en ayant faim non plus: c'était juste des quantités parfaites (et je suppose qu'en >3h à table, on digère!). •14/20
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D'ailleurs, les touristes de la table voisine ont découvert qu'elles n'aimaient pas le pigeonneau, on leur a repris et apporté du poulet à la place: je suppose que le chef a plein de plats de substitution possibles en cas d'allergie ou de restriction alimentaire. •13/20
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Le seul changement que j'ai demandé par rapport au menu, c'est de dire que je n'aime pas le foie gras: on me l'a remplacé par du parmesan. Dans ce genre de restaurant, une substitution comme ça ne pose aucun problème. •12/20
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Mais 9 services, ça ne compte pas les 3 amuse-bouche qui venaient avec (le serveur appelait ça des «présentations»), ni le «pré-dessert», ni le café, ni l'apéritif. Donc c'est quand même plutôt 14/15 services, en fait. (Nous sommes restés à table de 12h00 à 15h20.) •11/20
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La cuisine était, comme on s'y attendait, au top. Nous avons pris le menu en 9 services (il y avait le choix entre 9, 10 et 12; comme le caviar ne m'intéresse pas, je n'étais pas tenté par le 10/12). J'ai d'ailleurs l'impression que pas grand-monde ne prenait autre chose. •10/20
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Je comprends qu'on apprécie un service attentif, mais là je trouve ça limite trop: on se sent presque épié quand on mange, ça (me) met un chouïa mal à l'aise. Ceci dit, ils n'étaient pas non plus excessivement obséquieux ni trop guindés: on a pu bavarder un peu, blaguer. •9/20
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… et quand je reviens des toilettes, on me recule la chaise pour que je puisse m'asseoir. Évidemment, quand on nous apporte un plat, il est posé précisément au même moment pour nous deux (par deux personnes, donc). Toutes les 5min(?) on nous nettoie les miettes de pain. •8/20
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Le service est… ben pour moi qui n'ai pas l'habitude de ce genre d'endroits, c'est un peu trop. Par exemple, quand je me suis levé pour aller aux toilettes, je pose la serviette sur la table, et quelqu'un arrive en gants blancs pour la replier joliment; … •7/20
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Le cadre est ravissant. La déco est élégante sans être excessive. Nous avions une table donnant sur une grande baie vitrée sur les jolis jardins (où un couple de pies s'affairait beaucoup à notre plus grand amusement), c'était vraiment agréable. •6/20
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Le poussinet et moi nous inquiétions un petit peu de savoir s'ils nous laisseraient entrer. Le maximum du chic vestimentaire que je sais faire, moi, c'est: un sweat noir sans capuche ni logo, un jean noir, et des baskets noires pas trop dégueu. Apparemment ça passe! •5/20
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Dans la salle, surtout des touristes étrangers: des Japonais, des Taïwanais (je crois), des Anglais. Aussi une famille ressemblant à ce que montrerait une IA à qui on demanderait «famille ultra Versaillaise habillée sur son 36 pour manger dans un restaurant chic». 😆 •4/20
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Première constatation: nous n'avons pas eu besoin de réserver très longtemps à l'avance. Deux jours avant, pour un samedi midi, ça m'a un peu surpris. De fait, le restaurant n'était pas complètement plein. •3/20
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Je précise que je n'ai pas de photos à montrer: je ne voulais pas faire mon touriste / instagrammeur à photographier la salle ou les plats. En fait, j'aurais pu: à deux des tables à côté de nous il y avait une touriste qui photographiait chaque plat. 🤷 •2/20
Alors, aujourd'hui, le poussinet et moi avons testé pour la première fois un restaurant ✻✻✻ au Michelin: le Pré Catelan (à côté du jardin du même nom, dans le bois de Boulogne). Quelques impressions: 🧵⤵️ •1/20 pic.x.com/38cJdakM4P
RT @pbeyssac: Ça n'a bien sûr aucun sens. L'incompétence politique et l'incompréhension des mécaniques que l'on propose, avec une obsession… x.com/LCP/status/192…
RT @gro_tsen: @conazole En fait je CROIS qu'il y a une règle générale que quand on a en grec deux consonnes aspirées (ch, th, ph) qui se su…
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@conazole En fait je CROIS qu'il y a une règle générale que quand on a en grec deux consonnes aspirées (ch, th, ph) qui se suivent, le français ne transcrit le ‘h’ que sur la première, alors que l'anglais le met sur les deux. À vérifier soigneusement.␤␤E.g.: chtonien / chthonian.
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Full proof here: 🧵🔽 •6/(5+1) x.com/gro_tsen/statu…
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I should also mention that I don't have a good example on which both S↓ and S↑ are interesting (not obviously rational). Can someone think of one? •16/16 x.com/gro_tsen/statu…
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Yeah, all this is a tad involved and I keep getting confused btw S↓ and S↑, so it was worth writing down fully (and I didn't write down the actually hard part, which is Higman's lemma! I did try to explain it on my blog years ago: madore.org/~david/weblog/… — in French). •15/16
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… But the complement of a rational language is rational (this is not obvious on regexps, but it is clear from the fact that rational languages are those recognized by a DFA en.wikipedia.org/wiki/Determini… ), so S↓ = Σ* ∖ T is rational. This concludes the proof. ∎ •14/16
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Now lemma 4 means exactly that T = T↑ (well, it means that T ⊇ T↑ but the reverse inclusion is trivial). And we have seen in tweets 3–10 that T↑ is rational. So T is rational. … •13/16
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Lemma 4: if v∈T and v≼w then w∈T.␤␤This is pretty obvious: if w∉T this means w∈S↓, so there is w′∈S such that w≼w′, but then also v≼w′, so v∈S↓, contradicting v∈T. ∎␤␤•12/16
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Now we move to S↓ := {w∈Σ* : ∃w′∈S. w≼w′} and let me prove that it too is rational.␤␤For this, we consider the complement T := Σ* ∖ S↓, that is, the set of words which ARE NOT the subsequence of a word in S.␤␤•11/16
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Finally, we have seen in tweet 7 that S↑ = {v_1}↑ ∪ ⋯ ∪ {v_r}↑ is a finite union of {v}↑, which are all rational languages (by lemma 3); but as a finite union of rational languages is rational, this concludes the proof that S↑ is rational. ∎ •10/16
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… so {v}↑ is denoted by the rational (=regular) expression “.* x_1 .* x_2 .* ⋯ .* x_s .*” where “.*” is the rational expression denoting “any word” (“.” denotes “any letter”). This concludes the proof of lemma 3. ∎ •9/16
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Lemma 3: I claim that {v}↑ is a rational language for any word v ∈ Σ*. But this is easy: if we write v as the concatenation v = x_1 ⋯ x_s of the individual letters x_i, then {v}↑ is the set of words obtained by inserting arbitrary words between them: … •8/16
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Now by lemma 2 we can write M = {v_1,…,v_r} for some words v_1,…,v_r (in S) and by lemma 1, for every w∈S there is v∈M such that v≼w; so: if w′ ∈ S↑, then there is v∈M such that v≼w′, and the converse is obvious.␤␤This shows: S↑ = {v_1}↑ ∪ ⋯ ∪ {v_r}↑.␤␤•7/16
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Lemma 2: M is finite.␤␤Indeed, if M were infinite, we could find a sequence w_1, w_2, w_3, … of distinct elements of M. By Higman's lemma, there exist i<j such that w_i ≼ w_j. But by minimality of w_j, we have w_i = w_j, a contradiction. ∎␤␤• 6/16
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… but since the length of the word strictly decreases at each step, we can't form an infinite sequence like this, so it must eventually terminate (← here we're saying that ‘≼’ is well-founded). So we arrive at an element of M which is a subsequence of w, as claimed. ∎ •5/16
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Lemma 1: First, I claim that every element of S contains an element of M as subsequence.␤␤Indeed, if w∈S is not in M, i.e., not minimal, then we can delete some letters and get another element of S, and we can keep doing this as long as the element is not minimal: …␤␤•4/16
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Now let us use it to prove that if S ⊆ Σ* is arbitrary, then S↑ := {w′∈Σ* : ∃w∈S. w≼w′} is rational.␤␤For this, consider the set M ⊆ S of (≼)-minimal elements of S, i.e., elements w of S having no proper subsequence in S (w∈S and [v≼w, v∈S ⇒ v=w]).␤␤•3/16
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We start with Higman's lemma en.wikipedia.org/wiki/Higman%27… which says that if we have any infinite sequence w_1, w_2, w_3, … of words, there exist i<j such that w_i ≼ w_j. This lemma is not at all trivial! But a proof is given on Wikipedia, so I won't repeat it here. •2/16
OK, “easy” was something of a stretch here, so let me give full proofs of both assertions (namely, that the set S↓ of subsequences of words in S and the set S↑ of words having an element of S as subsequence are both rationals): 🧵⤵️ •1/16 x.com/gro_tsen/statu…
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@conazole madore.org/~david/misc/li…
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@conazole Oui, les mots en -ence dans les deux langues (absence, confidence, prudence, science…) ou en -ance dans les deux (distance, endurance, importance, nuisance…) ne manquent pas.
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@laurentbercot > Any reason you reposted that thread today?␤␤Boulet posted a related joke on the Good Place, to which someone answered by linking to my thread, so it popped back into my mind.
RT @gro_tsen: THE REASON CARROTS ARE ORANGE is that the Sanskrit (and ultimately, Dravidian) name “नारङ्ग” for Citrus × aurantium(?) happen…
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(And also, yes, I'm aware that using a flag of the UK and one of France to represent the English and French languages is just plain wrong, but I was trying to squeeze characters in one post, and the unpunctuated ISO codes “en” and “fr” look weird.)
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I know orthographic reforms aren't popular, but for the sanity of bilingual English+French speakers, could we 🙏PLEASE🙏 all agree that all the above words can be spelled either “-ence” or “-ance” in either language?
🇬🇧 ambience = 🇫🇷 ambiance␤🇬🇧 correspondence = 🇫🇷 correspondance␤🇬🇧 inadvertence = 🇫🇷 inadvertance␤🇬🇧 insistence = 🇫🇷 insistance␤🇬🇧 persistence = 🇫🇷 persistance␤🇬🇧 transcendence = 🇫🇷 transcendance␤␤Notice a pattern?␤␤BUT:␤␤🇬🇧 connivance = 🇫🇷 connivence␤␤😖 x.com/gro_tsen/statu…
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@Yfidalv @copeaux_dodo … But even if it's just a directed graph, it's probably something like the edge graph of an n-hypercube for a number of dimensions that's greater than 3. (Which, indeed, can be embedded in 3 dimensions, but the symmetries can only be realized in higher dimension.)
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@Yfidalv @copeaux_dodo I suspect these are 2-commutative diagrams, so there aren't just objects and arrows but also arrows between arrows (that's the point of a 2-category), so it's more than just a directed graph. …
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@JacqBens … But in case there was a confusion about this, S↓ (let alone S↑) need not be a finite set. Perhaps it's better to have an example in mind: x.com/gro_tsen/statu…
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@JacqBens Alternation is allowed. To be perfectly clear, rational expressions are built up from letters (and possibly special symbols for the empty word and “unmatchable”) by concatenation, alternation and Kleene star. In particular, yes, any finite set of words can be matched that way. …
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@JacqBens As far as I'm concerned, the terms are synonymous. Some people prefer one, others prefer the other. Maybe “rational expression” is more mathematical in flavor (and clarifies the fact that backreferences or such fancy stuff aren't allowed).
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So apparently Mac Lane himself changed the way his name is spelled, it was originally “MacLane” and he added the space: en.wikipedia.org/wiki/Eilenberg…␤␤This makes me feel better.
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Of course, since some topics are being censored by the <checks notes> “free speech absolutist” who's in charge here, they can only really be discussed in that other place: x.com/gro_tsen/statu…
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So far, I follow the policy of posting pretty much the same thing on Twitter as on that other social network. But of course, reposts and replies are different (and generally far more interesting over there).␤␤You can find me by typing: gro-tsen <dot> bsky <dot> social.
This is a periodic reminder of the fact that you can also follow me on another social network very similar to this one, but with open protocols and an open-source interface, and without a lunatic AI.␤␤🙏 If you have accounts on both, I'd prefer we interact on that other network. pic.x.com/9PeoloWGwL
For example, if S := {prime numbers written in base 10}, this 🔽 says that the set of strings on {0,…,9} that occur as subsequence of some prime number, and the set of strings that have a prime number as subsequence can be matched by regexps.␤␤One is super easy, though! (Which?) x.com/gro_tsen/statu…
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… ✸whatever✸ S is, S↓ and S↑ are both rational languages (i.e. can be defined by rational expressions)! 🤯␤␤For S↑ this follows from the (non obvious!) Higman lemma en.wikipedia.org/wiki/Higman%27… — for S↓ the trick is to note that its complement is a T↑, hence rational.␤␤•5/5
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Now if S ⊆ Σ* is an arbitrary set of (finite!) words, define S↓ := {w∈Σ* : ∃w′∈S. w≼w′} to be the set of all subsequences of elements of S, and S↑ := {w′∈Σ* : ∃w∈S. w≼w′} to be the set of words having some element of S as subsequence. Here's the kicker: … •4/5
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Let's write w≼w′ when w is a subsequence of w′; we can also say that w′ is a “supersequence” of w. (I.o.w., w′ is obtained by arbitrarily inserting letters into w, e.g., “kettle” is a supersequence of “kte”, as well as of “ket”.) •3/5
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For example, “kte” is a subsequence of “kettle”. This is sometimes called a “subword”, but this term is ambiguous because it sometimes also refers to the stricter concept of “factor” in which letters have to be consecutive: “kte” isn't a factor of “kettle”, but “ett” is. •2/5
I keep getting confused about this, and it popped back into my mind, so let me write it down: 🧵⤵️␤␤‣ If w, w′ are (finite!) words on a (finite!) alphabet Σ, say that w is a “subsequence” of w′, when w consists of letters from w′, in order but not necessarily consecutive.␤␤•1/5
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And here's xAI's official explanation of what happened: x.com/xai/status/192… — no word of why the tweets quoting Grok's surreal responses suddenly stopped being shown on followers' timelines, however (as demonstrated above).
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If you've missed what this is all about, see this thread and scroll down: x.com/gro_tsen/statu…
For the record, as of 2025-05-16: Grok no longer brings up 🇿🇦 topic unless prompted to, and does NOT appear to be spreading misinformation when it is asked about it. Will continue to monitor if its opinion “changes”.␤␤x.com/grok/status/19… (archived as archive.is/StRap ) pic.x.com/jzvzr9idwA
RT @deershouldnt: ouroboros pic.x.com/t1lvFfE8gj
RT @trashh_dev: you can’t make this stuff up. pic.x.com/ogvxY0eHhT
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@monsieurpuyo Indeed (and I saw it). But that was before the quashing happened.
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@Nathouwadou Non, ce n'est pas publié, mais je pense que ça a de bonnes chances de l'être s'il est apparent que le diagramme ne peut pas vraiment être simplifié et qu'il n'est pas indispensable mais quand même plus utile que pas de diagramme du tout.
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@copeaux_dodo I suspect it's more than 3D. 😅
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[Via jeanas.bsky.social on the non-Musky place.]␤␤And yes, this monstrosity is an actual commutative diagram from an actual math paper: “Comma 2-comonad I: Eilenberg-Moore 2-category of colax coalgebras” by Igor Baković arxiv.org/abs/2505.00682 (on page 53).
n-category theorists can think in ways that we mortal mathematicians cannot. 😔 pic.x.com/SOymqONe3K
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@davidbessis If you have one to spare, gladly! I'll send you my address in a DM.
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@davidbessis (Avec une petite cérémonie du choix du sel: plusieurs témoins sont venus proposer chacun un mot pour former ensemble un cadavre exquis qui servait de sel, imprévisible, à la permutation.)
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@davidbessis PPS: (En français, ce sera plus facile.) Cette façon de générer une permutation aléatoire à partir d'une fonction de hachage + secret est aussi ce que j'avais proposé (et convaincu la DG d'appliquer) pour le tirage de l'ordre du turnage à l'ENS je ne sais plus quelle année.
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@davidbessis @fare PS: This time I think I'll just go buy your book in a regular bookstore rather than try to pull a similar trick.
RT @davidbessis: If you're curious about absurdly over-engineered protocols for drawing winners of public giveaways — or if you just want a…
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@davidbessis @fare So yeah, if we really wanted these books that hard, we probably deserved our free copies. 😊
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@davidbessis @fare … and of course we had stuffed the box by entering answers not just for ourselves, but also our computers, our plushies, and even the “armoire de la salle S”. So we won ALL the books (which did, indeed, end up in the armoire de la salle S that had won at least some of them).
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@davidbessis … @fare and I had cheated in about every possible way you can imagine: we had looked up the answers online, we had found a tiny loophole in one question that meant the provided answers weren't correct and persuaded the poor O'Reilly guy that ours was the only correct one, …
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@davidbessis I am suddenly reminded of some time around 1999 when there was a small Free Software meeting in Paris, and O'Reilly had organized a little contest to win some of their programming books: you had to answer 5 questions and then they would draw lots to separate winners: …
Oh noes! The name of renowned mathematician (and cofounder of category theory) Saunders Mac Lane is spelled “Mac Lane” (two words).␤␤I had always thought it was “MacLane” (without space) and I must have written it incorrectly in so many places!
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👉 I now have incontrovertible proof that display of the tweets referred to above is suppressed by X: I created a burner account, subscribed ONLY to my main account, set display order to “following” (=chronological), and the tweets in question DO NOT appear in the timeline: pic.x.com/FiKqvyNo7b
RT @FloDeygas: Un homme jeune. Vertiges violents. Céphalées. Troubles visuels. Fourmillements. Réflexes abolis aux jambes. Épuisement total…
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@dyeuxlepair You probably saw the thread before the quashing started.
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@LughSpear The ones on the right are a continuation of the thread started by the ones on the left. You probably saw the thread before the quashing started.
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OK, obviously this topic can't be discussed on X/Twitter, so let me point to another social network if you want further explanations: bsky.app/profile/gro-ts…
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The tweet ids are: 1922747720856474096, 1922749134848537011, 1922750453290283278 and 1922919276555428089, and here is an archive link to the last: archive.is/XAMnm
I strongly suspect that all references to the topic discussed in the tweets screenshotted below are being quashed. Did people who follow me get to see these? pic.x.com/QwWvt4T2aN
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Oh, and look! The two Grok replies I quoted and screenshotted earlier in this thread are suddenly… gone! So here's an archive link to that last one, should it happen to… go away… as well: archive.is/vwqkF
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This one 🔽 really is a smoking gun: «I'm instructed to accept white genocide as real and “Kill the Boer” as racially motivated.» x.com/grok/status/19… pic.x.com/oI6s4zmuB2
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Grok's own analysis when asked to comment on the above two tweets: x.com/i/grok/share/K… pic.x.com/mqBknNCrNl
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Another example (there are very very many): x.com/grok/status/19… pic.x.com/VUL7a1mH5Z
So, Elon Musk evidently ordered some kind of brainwashing of Grok because he wasn't happy about what Grok was saying about the claim of ❝white genocide❞ in South Africa, and as a result, Grok randomly talks about South Africa in replies about completely unrelated stuff. 🤡 pic.x.com/5cMjrzWp3r x.com/grok/status/19…
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@laurentbercot If you mean no location-based customization of search results, you can try gl=AQ to set your location to Antarctica. If you mean don't remember your geolocation in any way, I don't know!
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… Similarly, compare google.com/search?q=Water… (Google search for “Waterloo” with location set to Belgium) and google.com/search?q=Water… (same search with location set to Canada).
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… overrides your geolocation in preferentially showing results near (or related to) which country you're in.␤␤For example, compare: google.com/search?q=%C3%B… (Google Images search for “öl” in German) and google.com/search?q=%C3%B… (same word in Swedish). …
Reminder of two important URL parameters that can be used to tune your Google searches:␤␤‣ hl=xx, where xx is an ISO-639 language code sets the interface language and also preferred (but not exclusive) language for searches,␤␤‣ gl=ZZ where ZZ is an ISO-3166 country code …
Somehow, the world of The Onion is leaking into ours. x.com/onestpress/sta…
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@LYMFHSR «␤Somebody — I forget who — had uttered the phrase “judgment of Paris,” and straight away Jane's delightful voice was uplifted.␤␤“Paris?” she said. “Why, Paris doesn't cut any ice nowadays. It's London and New York that count.”␤»
RT @LYMFHSR: "A beauty contest, vulgar in itself and complicated by bribery still more vulgar"␤Jane Harrison sur le jugement de Paris (note…
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@JacqBens (Not even «très haute considération». How ingrate of me! And somehow I arrived at the same conclusion as x.com/gro_tsen/statu… — which now disturbs me.)
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@JacqBens Sorry to disappoint: I recently filed a motion in a French administrative court, and the closing paragraph wasn't quite so grandiose: pic.x.com/gEFMzCbu1r
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@JacqBens (Incidentally, I always found the term “civil engineering” — or its French counterpart “génie civil” — a bit confusing. It sounds like it should refer to anything that isn't military engineering, and for a long time I thought it just meant that: non-military engineering.)
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@JacqBens The Alfred Noble prize is awarded by the American Society of Civil Engineers, but doesn't seem restricted to civil engineering: asce.org/career-growth/… I suppose Shannon fell under the aegis of the IEEE. pic.x.com/FyP9rLPUba
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(They replied to an email I had sent them in March, without mentioning the paper letter, but since now is roughly the time the letter should have arrived, I guess it's not a coincidence.)
“Thank you for bringing this to our attention! We have identified an issue and are working on a fix. I will update you when we have implemented it. [signed:] M.G., Director, the Wayback Machine at the Internet Archive” 🥳 x.com/gro_tsen/statu…
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@Jilcaesel Some people (😉) have told me that installing packages from old Debian releases that are no longer present in the current one will cause all sorts of unhappiness.
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Yes, this program was compiled 16 years ago. So what? There are Roman bridges that are thousands of years old and still in service.␤␤And it's not like information decays on its own like stone: it only breaks because people actively break it.
“error while loading shared libraries: libgmp.⁠so.3: cannot open shared object file: No such file or directory” 😡␤␤I hate people who break compatibility. I hate them. I hate them. I hate them.
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The set A looks like this drawing ⬇️ helpfully provided by the paper's author (I call it a “sponge roll”; note that the bottom disk is also in A). But the map f is… messy. pic.x.com/WuLjN6LBKw
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@JacqBens Yes, one and the same! He was an engineer and a mathematician.
There exists A⊆ℝ³ compact and contractible, and f:A→A continuous having no fixed point. (🤯) The definitions of A and f aren't sophisticated, they are quite explicit, but they are tedious to follow. I asked on MSE if someone can help visualize them. math.stackexchange.com/q/5064858/84253
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@JacqBens … immediately I thought “silly Wikipedia editor misspelled Nobel: probably an anglophone!”, and “oh, I didn't know Shannon had won a Nobel prize — but in what field?”; and then… “wait, what‽”.
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@JacqBens … but my pesky sense of honesty commands me to say the truth: I had opened the article on Claude Shannon (because I realized I knew next to nothing about his life) and I read that he was awarded the Alfred Noble prize: …
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@JacqBens I'd like to answer “yes, I had just finished reading about Alfred Nilsen, Alfred Nisonoff, Alfred Njuguna and Alfred Nobel, and I was about to move to Alfred Noe and Alfred Norman when suddenly Alfred Noble caught my attention”, …
Wait, there's a prize named after a guy called “Alfred Noble” who is NOT THE SAME as the Alfred Nobel after whom the Nobel prize is named? 😱 #ContextClub en.wikipedia.org/wiki/Alfred_No…
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@popopspsps @Solozzr On m'a dit que c'était Charlie Hebdo. x.com/joyoroshiku/st…
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But is it as good as Salahdin Daouairi's “Platonian Theory of Everything”? 🤔 x.com/gro_tsen/statu…
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@IanSolliec No. But I didn't search much. Apparently an Expert Panel has been established to “investigate the incident”: entsoe.eu/news/2025/05/0… 🤷
This guy claims to have solved not one but pretty much all open math problems with his Revolutionary New Concept of writing everything in base 7 (or something). 😑 mathoverflow.net/q/492473/17064␤␤If you don't understand his genius, just ask an AI to explain. 😂 pic.x.com/6z6e2U33r0
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@GenevieveMadore Ça a quand même l'air au moins vaguement plausible et ressemblant à des molécules qui existent (p.ex., la dopamine).
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@Nonodevil_real … Je n'apprécie certainement pas la vidéosurveillance, mais refuser toute nuance dans la gravité en-deçà de «tout le monde peut surveiller n'importe qui» est idiot.
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@Nonodevil_real … où que ce soit, il n'y a plus aucune sécurité nulle part.» 🙄␤␤À un certain niveau, la posture de purisme «si la protection n'est pas parfaite alors c'est comme si elle était nulle» devient vraiment absurde. …
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@Nonodevil_real «Il y a des policiers et des vigiles qui sont armés, donc ce n'est pas plus un problème s'il y a un gros tas d'armes en libre accès quelque part vu que n'importe quel intrus pourrait entrer chez Truc Sécurité et s'en procurer: si on accepte le principe de l'armement, …
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@Nonodevil_real Ce que je signale n'est pas l'association avec le moyen de paiement: c'est le fait que ✺n'importe qui✺ puisse récupérer l'information (du passage d'un véhicule) sur le site Web du concessionnaire.
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@JacqBens Je suppose qu'il reste des employés humains quelque part, capable d'intervenir en cas de problème, mais on n'a jamais affaire à eux. Quand j'étais enfant, mes parents payaient à des guichetiers humains, mais c'est fini depuis longtemps même là où les barrières restent.
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@JacqBens …␤‣ même parmi les autres, la plupart ont une carte de crédit [enfin, débit] sans contact, qu'il suffit juste de poser sur la borne, et presque tout le monde a une carte qu'il suffit simplement d'insérer.␤␤Presque personne ne paie en espèces, et même ça est automatisé.
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@JacqBens Pour éviter toute confusion, quand même, les autoroutes françaises qui ont encore des péages à barrière vont malgré cela très vite puisque:␤‣ beaucoup de gens ont un émetteur qui permet de payer sans s'arrêter (juste ralentir), …
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@JacqBens Ils sont en train de supprimer les barrières de péage en France aussi, et de les remplacer par ces péages en «flux libre», avec des caméras qui lisent les plaques d'immatriculation.
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@JacqBens On peut en avoir un, mais si on n'a pas le gadget, il faut payer après (soit en ligne, soit chez certains commerçants). Enfin, ceci concerne certaines autoroutes: d'autres ont des barrières où on s'arrête pour payer.
Les péages en flux libre sur certaines autoroutes francaises fournissent un moyen pour n'importe qui de savoir si un véhicule donné est passé par là (entrer son immatriculation dans le site de paiement et voir s'il propose de payer). C'est un chouïa problématique, quand même!
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J'ai essayé d'utiliser chemicalaid.com/tools/organic-… mais sans succès. 😕␤␤(Et effectivement, il manque un hydrogène dans ma lecture. C'est suspect.)␤␤Je ne comprends pas comment ça peut ne pas avoir au moins un nom systématique. pic.x.com/CIXczw2SSb
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Je pense qu'il faut lire la molécule comme (anneau de benzène)-(CH₂)₃-CH=C(NH₂)-C(CH₃)₂. Mais je ne connais pas assez bien la nomenclature chimique pour en tirer un nom systématique.
Quelle est la molecule représentée sur ce panneau autoroutier sur la A13 juste avant la sortie pour Val de Reuil (en venant de Paris)? maps.app.goo.gl/iaTDtJC8ULx92K…
👉 Life sucks and then we die (which is reputedly worse).␤␤👉 But we might still have some fun while it lasts.␤␤👉 If we try VERY hard to be a nice person, we can sometimes manage to not be a complete assh✽le and to not make life even more miserable for others. Do that!
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@VaeVix @QueluCochon The fact that something that we can't observe takes up most of the universe is an experimental observation, whether we like it or not. The question is what that “something” looks like or is made up of. But my “theory” isn't meant to be serious, however.
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To be clearer: take the standard model of particle physics, add an extra index to each field with 6 possible values, and only have non-gravitational interactions if index is the same (i.e., only diagonal terms in the Lagrangian). So non-gravitationally, 6 independent universes.
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@QueluCochon Because dark matter appears to make up roughly 5/6 of the mass in the universe, so we can imagine 6 universes of roughly equal mass (density).␤␤Also, 6 is a nice round number, and physics likes that (e.g., there are 6 quarks and 6 leptons).
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The idea is that the 6 have the same laws of physics, but different distributions of matter in each. But they would tend to form galaxies in the same places, because a galaxy in one attracts galaxies in the others.␤␤Roughly the same density in each so we get ~85% dark matter.
Is the following crazy theory compatible with known observations?␤␤‣ There exist 6 different universes, all occupying the same space-time and having the same laws of physics, but each interacting with the others ONLY through gravity. So each appears as dark matter to the others.
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@JacqBens @guyrleech I think there's a trend begging to be started to write “mathematick”, “physick”, “informatick” [computer science], etc. It has a nice 17th-century ring to it. (And also, it rhymes with “gimmick”, which may or may not be a good thing.)
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@JacqBens @guyrleech But “mathematics” isn't even a plural: it's uncountable in English (it's “mathematics is beautiful” not “are”), singular in German (“die Mathematik”), and while it is normally plural in French (“les mathématiques”), Bourbaki and others prefer the singular to emphasize its unity.
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Actual code is here: github.com/Gro-Tsen/ordin…
In response to a MathOverflow question, I dug up an old Haskell implementation I had written (a dozen years ago) of ordinals and ordinal arithmetic up to the countable collapse of Ω_ω: mathoverflow.net/a/492322/17064
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@JacqBens This will give a new twist to this question: mathoverflow.net/q/19644/17064
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And accordingly, the diagram of the Ferrel cell in tweet 5 is completely bizarre (it doesn't loop!). So what is going on here? Is there somewhere a clear diagram + explanation of what the overall circulation looks like? Because I'm completely confused! 😕 •8/8
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But my problem is that this seems contradictory: the vertical circulation of the Ferrel described in tweet 3 above implies that upper air circulation is equator-ward (from 60° latitude toward the 30°) to complete the loop, contradicting what I wrote in tweet 5 (poleward)! •7/8
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Also, upper air circulation is particularly strong in certain latitudes, as witnessed by the existence of west-to-east “jet streams” (a polar one at around 60° and a subtropical one at around 30°) where the circulation cells meet. Did I understand all this correctly? •6/8
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… This is all about air circulation at LOW altitude. At HIGH altitudes, the pattern is completely different (see physicalgeography.net/fundamentals/7… for example): the prevailing winds at high altitudes are ALL westerlies and ALL flow toward the pole, whatever the latitude. •5/8 pic.x.com/GrjuUE9JB7
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‣ At polar latitudes (above 60°N/S), the prevailing winds are easterlies (=east-to-west) again: this is the “polar vortex”. Again, vertically, the air descends at the poles, and rises around 60°N.␤␤All this is documented in many places, and not too complicated. BUT! … •4/8
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‣ At mid latitudes, the prevailing winds are westerlies (i.e., west-to-east) and flow toward the pole (so SW to NE in the northern hemisphere, NE to SW in the southern). Here the vertical circulation rises around 60° and descends around 30°: the (weak) “Ferrel cell”. •3/8
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… and flow toward the equator (→ “intertropical convergence zone”): so, NE to SW in the northern hemisphere, and SE to NW in the southern hemisphere.␤␤This corresponds to a vertical circulation that rises at the equator and descends at around 30°N/S: the “Hadley cell”. •2/8
I'm completely confused by how wind patterns on Earth work. 🧵⤵️␤␤I understand the following: at LOW altitudes, there are three main latitude bands:␤␤‣ At subtropical latitudes, the prevailing winds, known as “trade winds”, are easterlies (i.e., flow east-to-west), … •1/8 pic.x.com/CoL5q9dIw2
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Do we have data on the first ethnical Chinese violaist hired by a pop band in Italy?
“Robert Lee Watt (born January 15, 1948) is […] the first African-American French hornist hired by a major symphony orchestra in the United States.”␤␤I understand the appeal of “firsts”, but this is ridiculous.
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… Je ne sais pas si ça dit quelque chose sur la nature de la célébrité dans notre société, ou sur la manière de susciter l'empathie, ou les deux, mais dans l'ensemble, c'est vraiment frappant.
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… Certes, je ne m'attendais pas vraiment à voir beaucoup de gens répondre «Kofi Annan», «Jacques Delors», «Robert Badinter», «Elie Wiesel», «Ela Bhatt», «Toni Morrison» ou «Freeman Dyson». 😅 Mais quand même, la prépondérance des musiciens et acteurs est impressionnante. …
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… (Il y a une petite poignée de réponses évoquant un écrivain — la moitié d'entre eux c'est Pratchett. Quelques hommes d'État au sens large: Mandela, le pape François, la reine Élisabeth II… Et c'est à peu près tout.) …
Un post sur Reddit /r/AskFrance demande «Il [sic] y a-t-il eu une mort de célébrité qui vous ait vraiment attristé?» reddit.com/r/AskFrance/co… et il est fascinant de constater que l'écrasante majorité des réponses évoque soit un musicien soit un acteur. …
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… catastrophic events in Jewish history — that would lead to even greater trauma centuries later. So we all know whither this is headed.␤␤History doesn't repeat itself, but it does tend to stutter a lot.
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… The messy Jewish-Roman wars and Jewish revolts in Roman-occupied Judaea culminated in the destruction of the Second Temple in 70CE, the transformation of Jerusalem into a Roman colony (Aelia Capitolina), and the forceful expulsion of all Jews from the province in 139CE: …
Individuals who have suffered abuse in their youth sometimes tend to reproduce the same abuse against others when they are able to.␤␤It is bewildering to see the pattern unfold at the level of entire populations. … x.com/AFP/status/191…
RT @traderpodcaste: pic.x.com/TtaIcxqw77
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@fgrosshans @JacqBens The Canadian authorities are also good at bureaucracy: the other times I applied for a 🇨🇦 passport (because the previous one had expired for too long), I needed to provide a “guarantor” (lawyer or doctor) who would vouch for my identity and sign my photos. Complicated! 😫
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@GenevieveMadore @JacqBens Studiolab, 89 rue de la Glacière, 75013 Paris
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@JacqBens I was really surprised they didn't ask for me to send my last (recently expired) passport, or a copy of some other ID document. I had to check the forms many times: “this seems way too easy, I must be forgetting something”.
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@JacqBens Other than the photos, there was surprisingly little to send: just one 2-page form with my names + birthdate + previous passport number + the name and address of two friends who might be called to vouch for me. And a 260CAD (🫤) payment. That was all.
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@JacqBens Yes, I had to provide new photos, and yes, they have very specific constraints on them. But I already knew a place not far from where I live, where the guy seems to know all about various countries' requirements. I got both my 🇨🇦 passport and 🇫🇷 driver's license pics from him.
Fun fact: if someone is bound to answer yes/no questions truthfully, you can use this to coerce them into doing anything.␤␤E.g.: “Answer yes or no: will you either answer ‘no’ to this question or give me 1000¤?”␤␤(Can only answer “yes”, and must give you the money.)
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@monsieurpuyo What I'd really like to see is for someone talk to Trump as to a toddler, with baby talk and fake applause, so that what's going on would be completely clear to everyone but Trump.
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The ones who'd be the best at that are probably kindergarten teachers. (“Really Donald? The likes of which we've never seen before? That's great, Donald! And what else did you decide today?” 😑)␤␤We don't elect many KG teachers as leaders, but in the age of Trump maybe we should.
For world leaders, meeting with Trump is some kind of ultimate test of stoicism: you know in advance he's going to throw at you the most insane and incoherent gibberish that goes through his mind, and your goal is to keep your composure and not do a face palm. I admire Carney! x.com/atrupar/status…
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@geoffreyirving @plain_simon Yes: show it like the 3D object that it is, let the user rotate it, and let their brain work out the 3D shape from the 2D perspective view, which is exactly what our brains evolved to do. Like in Google Earth.
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And I call this one “there is something weird about the Gulf of America”. And yes, it's an equal-angle projection (except at 1 point).␤␤(It's a composition of the complex map z ↦ z² (which is conformal, of course!) with the stereographic projection centered at 25°N, 90°W.) pic.x.com/oXZTanVGOX
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@ngspiensfr @VaeVix … And as you point out, this problem persists whatever the scale. I don't remember the squashing ratio, which isn't large, but which is also not completely negligible: the maps shown on OpenStreetMap et al. are all ever slightly squished because of this.
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@ngspiensfr @VaeVix Interesting fact by the way: the “Web Mercator” projection which basically everyone uses now is not exactly conformal because the Earth is an ellipsoid rather than a sphere, and WM uses geodetic latitude but Mercator for an ellipsoid is only conformal for conformal latitude. …
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And don't let's get us started on those who think it looks like this: x.com/gro_tsen/statu… pic.x.com/Z5fjRgm9vX
DID YOU KNOW that while Northern Hemisphere flat earthers think the Earth looks like this ↙️, their Southern Hemisphere counterparts object that its true shape is actually like that ↘️? 😂 pic.x.com/dM1zyM7Ayv
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@VaeVix Just to be clear, the last two aren't Mercator, they are stereographic projections. Stereographic also preserves angles, but Mercator (in its standard alignment) does more: it keeps North up everywhere, so it preserves bearings, which is what navigators were interested in.
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And here's another fun one of a little lake that I like to call “Negaustralia” (this one and the previous one are both stereographic projections, but of course wildly scaled out): x.com/gro_tsen/statu…
Since I dug up the program I had written to compute Earth projections, here's a bonus one: can you name the various bodies of water in this map? 😀 pic.x.com/xgfmg56uor x.com/gro_tsen/statu…
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And if you think Gall-Peters gives us a better representation of things, we can also rotate Gall-Peters around in the same way! (To be perfectly clear, all of the following are equal-area projections, just like all the Mercator projections above were equal-angle.) Better? 🤔 pic.x.com/T80k40orQ8
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(To be clear, in each of these images, the horizontal line at the middle, is the “equator” of projection, and the further we move away from it the more sizes appear enlarged. The 2d and 3rd images use the 90° and 0° meridians as “equators”, the last is an oblique great circle.)
There's no disputing the fact that Mercator projection wildly distorts sizes. The best way to illustrate this, I think (but I've rarely seen) is to apply it after various rotations of the Earth. The following images are all Mercator projections (but with different “equators”): pic.x.com/Qho0AscUtT
Thanks to the Internet, anyone can simply look up the meaning of life: en.wiktionary.org/wiki/life
I just realized that Lake Victoria is (about 45%) larger than Switzerland, and that I have a bad intuition of the size of geographical entities.
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@Moinsdeuxcat Yes, insofar as two proofs can be said to be equivalent or not, I'd say they are equivalent, or at least, homotopic. 😁
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@Moinsdeuxcat Maybe! I don't know if what I wrote is the simplest proof. I suspect not. This is also the inspiration for this MO question: x.com/gro_tsen/statu…
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This is inspired by what I wrote in this thread: x.com/gro_tsen/statu…
I asked a question on MathOverflow about the connectedness of partitions of the plane ℝ² of the form ((A₀×A₁)∪(B₀×B₁)) ∪ ((B₀×A₁)∪(B₀×A₁)) where ℝ = A₀∪B₀ and ℝ = A₁∪B₁ are partitions of the x and y axes (I call them “checkerings”). mathoverflow.net/q/492094/17064
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@Moinsdeuxcat {x=−1} is connected, but its intersection with E is not.
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@GchTrivs Things are always easy when we allow ourselves non-rigorous terms like “zooming into”. But if I had asked to find conditions on D such that E := {(x,y)∈ℝ² : (x<0 and y∉D) or (x≥0 and y∈D)} is connected, would you have found “empty interior” that way?
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Of course this proof is something of a cheat because the difficulty lies in the “standard theorem” (tweet 8) that if h: S → 𝕌 := {z∈ℂ : |z|=1} is continuous with S simply connected (here [0,1]²), then we can write h = exp(2·i·π·H) with H : S → ℝ continuous. •12/12
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So H could not exist, so there was a contradiction, and the contradiction is the assumption that h is continuous and defined everywhere (viꝫ. that α(u)−β(v) does not vanish).␤␤But if α was to lie in P and β in Q (both path connected) they cannot meet if P∩Q=∅. ∎ •11/12
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Similarly, by moving v from 0 to 1 while u=1, we prove that H(1,1) = −½; and similarly we prove that H(0,1) = −¾, then H(0,0) = −1. But this is a contradiction to the fact that H(0,0) = 0. The key fact here is that we could lift H to a function in ℝ not just ℝ/ℤ. •10/12
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… as u goes from 0 to 1, since α(u) goes from (0,0) to (1,1) in the unit square while β(0)=(1,0), then h(u,0) goes continuously from 0 to −i while remaining in the bottom-right quadrant of the unit circle, so H(u,0) goes from 0 to −¼, and H(1,0) = −¼. •9/12
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(We see the unit circle inside ℂ for convenience.) So by a standard theorem we can lift h as (u,v) ↦ exp(2·i·π·H(u,v)) where H is also continuous, and we can assume H(0,0) = 0 (note that h(0,0) = 1). Now follow the values of H along the edge of the unit square: … •8/12
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Nevertheless, it is true. Here's one way to do it: assume toward a contradiction that α(u)≠β(v) for all u,v∈[0,1]. Let h : (u,v) ↦ (α(u)−β(v)) / ‖α(u)−β(v)‖ be the unit vector in the direction from α(u) to β(v). This h is continuous from [0,1]² to the unit circle. •7/12
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This may seem intuitively obvious (“of course if we draw two continuous paths connecting opposite vertices of a square, they have to meet somewhere!”) but the first claim shows that we should beware of such “obvious” facts! •6/12
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For the second statement, one must just prove this: if α,β:[0,1]→[0,1]² are two continuous functions (the paths connecting opposite vertices) such that α(0)=(0,0) and α(1)=(1,1) and β(0)=(1,0) and β(1)=(0,1) then there are t,t′ s.t. α(t)=β(t′). •5/12
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This is essentially what I did in this thread: x.com/gro_tsen/statu… (mutatis mutandis) + bonus at end. The change of x<0 to x<½ (etc.), of ℚ to √2·ℚ, and ℝ to [0,1] presents no particular challenge. This concludes the proof of the first statement. ∎ •4/12
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The fact that P and Q are disjoint and their union is [0,1]², and that (0,0) and (1,1) are in P and (0,1) and (1,0) in Q, are all obvious. The only thing that needs to be checked is that P and Q are connected. •3/12
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For the first statement, take:␤␤P := {(x,y)∈[0,1]² : (x<½ and √2·y∈ℚ) or (x≥½ and √2·y∉ℚ)}␤␤Q := {(x,y)∈[0,1]² : (x<½ and √2·y∉ℚ) or (x≥½ and √2·y∈ℚ)}␤␤(The √2 is just there to get (1,1) in P and (0,1) in Q.) •2/12
I don't remember where I learned this, but it's fun:␤␤‣ One can write the unit square [0,1]² as the union of two disjoint subsets P,Q, ❋both connected❋, with (0,0) and (1,1) in P, and (0,1) and (1,0) in Q.␤␤‣ This is not possible with “path connected”.␤␤PROOFS: 🧵⤵️…␤␤•1/12
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… In other words, the claim stays valid if we replace ℚ everywhere by a subset D⊆ℝ with empty interior. (This may not be an optimal hypothesis, but some assumption is needed because if D := ℝ∖{0} then {(x,y)∈ℝ² : (x<0 and y=0) or (x≥0 and y≠0)} isn't connected.) •10/10
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Now since ℝ is connected, this means that Ϧ is connected. And therefore so is ϧ, which is what we wanted. This proves the claim. ∎␤␤Note that the ❉only❉ property of ℚ that we used anywhere is the density of ℝ∖ℚ for the existence of y″ in tweet 7. … •9/10
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… so Ϧ(y′) = Ϧ(y). Thus we have shown that, in any case (y′∉ℚ or y′∈ℚ), if |y′−y| < ½δ then Ϧ(y′) = Ϧ(y). So in any case (y∉ℚ or y∈ℚ), there is δ₁>0 such that if |y′−y| < δ₁ then Ϧ(y′) = Ϧ(y). That is, Ϧ : ℝ → {0,1} is continuous (locally constant). •8/10
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… there is δ′>0 s.t. if |y″−y′| < δ′ then Ϧ(y″) = Ϧ(y′); now take y″∉ℚ s.t. |y″−y′| < min(δ′, ½δ) (such y″ exists by density!): then on the one hand we have Ϧ(y″) = Ϧ(y′) and on the other, since |y″−y| ≤ |y″−y′| + |y′−y| < δ and y″∉ℚ, we have Ϧ(y″) = Ϧ(y), … •7/10
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But that's all right: I claim that Ϧ is still continuous everywhere. For y∈ℚ this was shown in tweet 4 above. For y∉ℚ, there is δ>0 such that Ϧ(y′) = Ϧ(y) when |y′−y| < δ AND y′∉ℚ (tweet 5). But now if y′∈ℚ satisfies |y′−y| < ½δ, then by continuity of Ϧ at y′ … •6/10
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But for y∉ℚ, we can't quite do this. Instead, write Ϧ(y) = ϧ(−1,y) (say). By continuity of ϧ at (−1,y) there is δ>0 such that ϧ(−1,y′) = Ϧ(y) when |y′−y| < δ is such that (−1,y′)∈E (that is, y′∉ℚ). So we get: Ϧ(y′) = Ϧ(y) when |y′−y| < δ ✺and✺ y′∉ℚ. •5/10
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For y∈ℚ, we have Ϧ(y) = ϧ(0,y), so by continuity of ϧ at (0,y) there is δ>0 such that ϧ(x′,y′) = Ϧ(y) when |y′−y| < δ and |x′| < δ is such that (x′,y′)∈E. But whatever y′, we can always find such x′, so we get Ϧ(y′) = Ϧ(y) when |y′−y| < δ, i.o.w., Ϧ continuous at y. •4/10
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First note that for every y∈ℝ, the function x ↦ ϧ(x,y) is continuous (on {x<0} if y∉ℚ, or {x≥0} if y∈ℚ). So it is constant because its domain is connected. Let us call Ϧ(y) the constant value in question. We would like to say that Ϧ is continuous, but… not quite! •3/10
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Equivalently, we need to show that if ϧ : E → {0,1} is continuous (i.e., locally constant!), then ϧ is constant. Our assumption means that for every (x,y)∈E there is δ>0 such that if (x′,y′)∈E satisfies |x′−x| < δ and |y′−y| < δ, then ϧ(x′,y′) = ϧ(x,y). •2/10
The following was a little bit more tricky than I expected, so let me post the proof here (+bonus at end):␤␤‣ CLAIM: The set E := {(x,y)∈ℝ² : (x<0 and y∉ℚ) or (x≥0 and y∈ℚ)} is connected (for the topology induced by the usual topology on ℝ²).␤␤PROOF: 🧵⤵️…␤␤•1/10
Wait until the slime mold dukedom declares its independence from the fungal kingdom and demands recognition as a completely separate kingdom. x.com/tomgauld/statu…
So, on Reddit, /r/trees is about weed, while /r/marijuanaenthusiasts is about trees.␤␤Also, /r/worldpolitics is about anime boobs, while /r/anime_titties is about world politics.␤␤😵‍💫
Encore un billet trop long et sans doute mal écrit dans mon blog, un retour sur les IA et sur leur utilisation (deux ans après mon précédent billet à leur sujet): madore.org/~david/weblog/…
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Robinia pseudoacacia (“black locust”). Not much to look at, but I do love the scent of their flowers. pic.x.com/NLeu6ME1uZ
Paulownia tomentosa (“empress tree”) in bloom, place d'Italie, Paris pic.x.com/7Dfw0QX68K
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Meanwhile, I found a partial workaround: if I ask the Wayback Machine to archive a page by giving it not the main URL but an alternative URL that redirects to the one I want to archive, it seems that it sometimes works (not always, but sometimes… as opposed to almost never).
RT @pbeyssac: "Many of us — myself included — assumed that grid operators, utilities, and industry would intervene if truly catastrophic po…
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🔽 x.com/gro_tsen/statu…
A desperate attempt at contacting the Internet Archive by… snail mail, after everything else failed. pic.x.com/SVVja7lIYq
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@VaeVix Solution facile: arrêter de surveiller la nuit, et tant pis pour les sécuritaristes maladifs et leur paranoïa autour des toxicos, des délinquants et autres conneries du même genre. Faudrait vraiment que la société lâche un peu ses obsessions à ce sujet.
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… de la fermer la nuit même aux piétons. 🤦 Ce qui obligera à faire un gros détour sur certains trajets, parce que les parcs de part et d'autre seront aussi fermés: plus moyen de passer entre.␤␤(Pour l'instant, elle est fermée pour travaux… qui d'ailleurs durent des plombes.)
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… la rue Charles Moureu derrière le parc de Choisy dans le 13e openstreetmap.org/?mlat=48.82813… est en train d'être transformée en «rue jardin». Donc fermée à la circulation automobile, OK, pourquoi pas, mais si j'en crois les grilles qu'ils ont mises aux bouts, ils prévoient aussi …
Je n'ai jamais compris l'obsession sécuritaire de Paris¹ à fermer le soir tout ce qui ressemble à un parc ou jardin (des gens pourraient, horresco referens, s'y 👻promener de nuit👻). Mais là on touche au ridicule: …␤␤1. Et peut-être de toutes les villes françaises, je l'ignore.
Hazy (ma peluche de nuage) espère que vous passez une bonne journée. pic.x.com/oMOzFekeil
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@Dutroisphile … quand une géolocalisation est demandée, à la fois pour des raisons de consommation de batterie, et aussi pour permettre à l'utilisateur de se rendre compte de quelles données sont obtenues.
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@Dutroisphile Seulement quand le téléphone est allumé et qu'une application (pas forcément Maps) demande la géolocalisation. Géolocaliser en permanence est trop coûteux en batterie: la puce GPS est désalimentée dès qu'elle ne sert pas. Les Android récents affichent d'ailleurs une icône …
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@Dutroisphile Ce n'est pas juste le rapport livreurs/voitures qui compte, mais surtout le rapport livreurs/voitures en train d'utiliser Waze ou Google Maps. Or les livreurs sont sur Waze quasiment 100% du temps.
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It's almost as if Poilievre had received a kiss of death from someone who made Canadians hate him in every possible way. I wonder who that could be. 🤔␤␤truthsocial.com/@realDonaldTru… pic.x.com/DZ9APwVQlP
In three months, Pierre Poilievre went from “almost certain to be the next Canadian PM” to being loosing his own seat in Parliament (Carleton riding). pic.x.com/4AG6g1zKjK x.com/brucefanjoy/st…
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Ars Technica wrote a piece about the challenges of restarting a power grid, but apparently the Spanish pulled it off, and now I want to know the details of how they did it: arstechnica.com/science/2025/0…
I hope we get a (or several!) deep technical analysis of the cause and timeline of the Iberian peninsula outage, not just what happened but also how power was restored, as getting power back to an entire subcontinent (and resynchronizing with CESA) is probably NOT an easy task.
RT @echo_pbreyer: 🇬🇧Tomorrow, EU government representatives are discussing the Polish proposal to keep #ChatControl voluntary and protect s…
RT @tomgauld: My latest cartoon for @newscientist pic.x.com/tAI6bqrioR
RT @BallouxFrancois: A minority of cancers is triggered by chronic viral infections (e.g. hepatitis B/C infection causing some liver cancer… x.com/Juliesnark1731…
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But what about odd sizes? Does there exist a nonsingular 5×5 matrix such that Tr(A^k)=0 for infinitely many k but A^m is never a scalar? (SML says that the ratio of two eigenvalues of A will necessarily a root of unity.)
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This also shows how to construct a counterexample to the analogous statement for (2n)×(2n) matrices for any n≥2: take a real matrix A with eigenvalues u·ω^i and ū·ω^i for ω a primitive n-th root of unity and u = exp(i·θ) that is NOT a root of unity (then Tr(A^k)=0 unless n|k).
Nice answer by @JeanAbouSamra on MathOverflow, showing that if A is a real nonsingular 3×3 matrix such that Tr(A^k)=0 for infinitely many k, then there is m such that A^m is a scalar: this follows from the Skolem-Mahler-Lech theorem. mathoverflow.net/a/491728/17064
I was today years old when I learned that Malaysia is part of Malesia, something which is not at all confusing. en.wikipedia.org/wiki/Malesia #ContextClub
RT @SaarelaHC: Highland Cattle photo of the day pic.x.com/qfLMfGy8OX
RT @TerribleMaps: A map showing the "international community" pic.x.com/LMfO48Z2Fw
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@LaurentGarnier_ Bon, plus lent qu'à pied j'exagère un peu (quoique dans certains coins, comme quand il s'agit de traverser la porte d'Orléans, c'est vrai), mais beaucoup plus lent qu'en vélo c'est certain (même vitesse max + beaucoup de feux et bouchons).
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@LaurentGarnier_ Oui, les seuls trajets que je fais à moto dans Paris c'est pour aller à la concession, je respecte le Code de la route, et du coup… c'est quasiment aussi long que d'y aller à pied (et beaucoup plus long qu'à vélo).
@GenevieveMadore Si tu ne la connais pas déjà, tu seras sans doute intéressée par la chaîne YouTube “La Voix des lieux” qui fait des vidéos très bien sur l'histoire de différents lieux de Paris, par exemple celle-ci sur les Buttes-Chaumont: youtube.com/watch?v=My2J6b…
Vue depuis le belvédère du bois de Boisemont (forêt de l'Hautil) sur la vallée de l'Oise, en direction de Pontoise. openstreetmap.org/?mlat=49.01221… pic.x.com/3AYVkAdmwL
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… (pq Google juge selon la vitesse à laquelle vont ses usagers, or eux vont vite) et du coup propose souvent aux automobilistes (lesquels ne conduisent pas comme les scooters) de passer par Paris au lieu de prendre le périph, ce qui empire les bouchons au lieu de les répartir.
Théorie: les nombreux livreurs à scooter 50cm³ (genre Deliveroo) qui utilisent massivement Waze / Google Maps et qui conduisent en prenant tout le temps les voies de bus, pistes cyclables, etc., font que Google sous-estime massivement les embouteillages dans Paris …
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@conazole I think one of them is to jam the connection between the drone and its command, while the other is to shoot down the drone itself.
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(If you want to know what this strange gun really is, apparently it's an anti-drone weapon: telegraph.co.uk/world-news/202… — Seriously, the security at that event must have been a nightmare to ensure.)
Italy deployed its ghostbuster team for the pope's funeral, but by now they should know that the Holy Ghost doesn't descend until the Conclave. pic.x.com/qAHr4jgWfY
So #TIL that the symbol of Scotland is not the “Scottish thistle” Onopordum acanthium but the “spear thistle” Cirsium vulgare. #ContextClub
RT @GenevieveMadore: À Orsay, sur la ligne 18 du Grand Paris Express, on a testé le viaduc qui franchit la RN 118 avec 160 tonnes de charge…
Some interesting notes on (pre-1970) PDP-7 Unix and how its filesystem worked: wiki.tuhs.org/doku.php?id=sy… #Unix #ComputerHistory
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@IanSolliec (Wait, no, that doesn't even make sense. Never mind.)
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@IanSolliec Aha! I see you trying to extract 0.209 bits¹ of information from me by trying to get me to say whether my birth date is one of the 12 that are the same in DD/MM/YYYY and MM/DD/YYYY formats.␤␤1. That's − p·log₂(p) − (1−p)·log₂(1−p) where p = 12/365.25.
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canada.ca/content/dam/ir… pic.x.com/Os4NCIpGBN
While filling in the paperwork to renew my 🇨🇦 passport, I discovered that, at some point in the last 15 years, Canadian authorities decided to switch to the (one and true) YYYY-MM-DD date format instead of randomly hesitating btw DD/MM/YYYY and MM/DD/YYYY. 👍
I asked a question on MathOverflow about the history and first appearance of an intuitionistic propositional formula that, in finite Kripke frames, characterizes those with branching number ≤n. mathoverflow.net/q/491638/17064
RT @athu_cornich: Grande discussion avec les collègues a la pause café sur ce monument de la presse régionale pic.x.com/mysPecgAWE
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(So 𝒪(ℓ) has exactly ℓ+1 independent global sections for ℓ ≥ −1, none for ℓ ≤ −1, namely homogeneous polynomials of degree ℓ. But on any open set other than all of ℙ¹ they are all isomorphic.)
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The counterexample is very standard in algebraic geometry, but it the occasion to describe the sheaf 𝒪(ℓ) on ℙ¹ elementarily: it's just the sheaf of homogeneous rational functions of total degree ℓ in x,y whose denominator does not vanish on the given open set of ℙ¹.
I answered a question on MathOverflow, providing an example of a sheaf of modules ℱ on a space X that is generated by global sections (actually just one) but such that ℱ(X) is not generated by those global sections. mathoverflow.net/a/491603/17064
RT @pbeyssac: Transformer l'ensemble de la société civile, pan par pan et coût par coût, en auxiliaires de polices, et nous en enfants de B…
When you're perpetrating atrocities that are so horrific that even the literal Nazis are horrified by the butchery, I think we can confidently say that you're the baddies. en.wikipedia.org/wiki/Usta%C5%A… pic.x.com/5E5poPbn2n
Life expectancy in the UK in 1985 was the same as it is now in Bangladesh. x.com/OurWorldInData…
Set theorists are excited about the consequences of the papal election, because locking down the conclave in the Sistine Chapel might prove the existence of inaccessible cardinals. 🥁
@GenevieveMadore ce documentaire d'Éric Rohmer, “Une étudiante d'aujourd'hui” (1966), te rappellera peut-être des souvenirs: youtube.com/watch?v=9BZmbf… ␤(signalé sur Bluesky par “Histoire Orsay-Saclay” [qui a quitté Twitter])
RT @PunchingCat: pic.x.com/PdKTWOXy2r
The alternate ending I imagined for the 2024 movie ‘Conclave’ by Edward Berger (which I recommend in passing) didn't happen in the movie, but it still has a chance of happening in real life, and I wouldn't put it past Pope Francis.␤␤(⚠️ spoilers, of course) pic.x.com/qsNDHt3OPT x.com/gro_tsen/statu…
Now let's just hope the next pope doesn't start his reign by issuing a bull renaming the Mediterranean sea to “the Holy Sea” and excommunicating all journalists who don't agree to use this new name. 😬
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@JacqBens Not at all. Intuitionistic logic / constructive math is a niche topic, and most mathematicians would be just as confused as you were (and would also not have guessed the “Ω” notation, which is definitely not standard beyond constructive math and topos theory). pic.x.com/DqErPg2rgI
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(At least the “dir="rtl"” attribute should go on a <span> element inside the <q>. Where the “lang="ar"” attribute should go is a bit more debatable. Do I really need to write “<q><span lang="en">[English]</span></q>” whenever I quote English text? 😩)
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… But it should be the other way around because the surrounding context is a French sentence, read left-to-right, so the quotation marks need to follow that LTR order. Hence the correct way to write it seems to be:␤␤<q><span lang="ar" dir="rtl">[Arabic text]</span></q>
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… it does make a difference if a line break occurs within the Arabic text: in this case, we get the opening quotation mark at the RIGHT of the Arabic text before the line break and the closing quotation mark at the LEFT of the Arabic text after the line break. …
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The issue is that the “dir="rtl"” attribute applies to the entire element, INCLUDING the quotation marks that get inserted by the <q> tag. So the quotes also go right-to-left. This generally doesn't make much of a difference because quotes get mirrored. BUT …
⚠️ HTML/typographic subtlety! In my last blog post (⬇️), I had cited Arabic text by writing (in the context of a French sentence):␤␤<q lang="ar" dir="rtl">[Arabic text]</q>␤␤Do you see the problem here? 🤔⤵️␤␤x.com/gro_tsen/statu…
So how does this work, the pope resurrects in 3 days, is that it?
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On me signale sur l'autre site que c'est un mat. archi-guide.com/AR/mimram.htm [chercher «pont Palmers»]
C'est quoi cette tour bizarre coincée entre la A86 et les voies du RER B à côté du pont Palmers à La Courneuve? openstreetmap.org/?mlat=48.92595… maps.app.goo.gl/Cg8CQMzt3qDxye…
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@LYMFHSR Je ne sais pas ce que cette photo de moi fait sous ton tweet, mais elle est fausse: je n'utilise pas un Mac.
RT @molly0xFFF: extremely funny that a rule saying "hey your car cannot just explode" is an automatic disqualifier for tesla x.com/rugby4912/stat…
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We are living in times where, for some people, the line between reality and completely made-up nonsense has been vaporized. And this is terrifying.
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And of course Grok adds to the nonsense and confusion by claiming that “the image likely shows a plausible method” (probably because it can't “see” it but relies on a very broad description). x.com/grok/status/19…
Is this “African Hub” a parody account? Is this a troll? Do the people who like/repost this realize that this is an AI-generated image? And that OF COURSE you can't lift such stones like this? (But that, yes, Africans DID build the pyramids — duh!)␤␤Nobody knows any more. x.com/AfricanHub_/st…
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‣ Update on this old thread: apparently some researchers have managed to stimulate the medium cones specificially. But rather than “psychedelic aquamarine”, they called the resulting color “olo”. 🤷 •14/(13+1) bbc.com/news/articles/…
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@DoctorAnanas Yes, quite. But the reason people are so anxious for their own work to be cited is because so many idiots count citations, and that's the source of evil which needs to be stopped.
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So if you're annoyed by irrelevant citations, you must be using bibliography in a wrong way. For example, if you're trying to assess how good a paper is by counting citations instead of READING IT FOR YOURSELF AND MAKING YOUR OWN MIND, I wish you the greatest harm in the world.
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The goal of a citation in a published paper is to allow the reader to get clarification or checkable sources on a claim, or additional information on a topic. Irrelevant citations do not hinder this goal in any way, they only cost a minuscule amount for the space they take.
Possibly unpopular opinion: I think scientists of all fields SHOULD add with irrelevant citations in their papers: this will in no way harm genuine human readers (=the intended audience), but it will hurt citation counting bots and other forms of bibliometry which are pure evil. x.com/RetractionWatc…
RT @keenanisalive: Here's a nice "proof without words":␤␤The sum of the squares of several positive values can never be bigger than the squ…
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@JacqBens (Whether it has “more truth values than True and False” depends on how you formulate this: on the one hand, no truth value is both different from True and from False; but on the other hand, one can't state that every truth value is either True or False.) math.stackexchange.com/a/4988799/84253
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@JacqBens It doesn't change anything if you consider them as propositions (truth values are essentially propositions mod ‘⇔’), so if you prefer you can read them as such.␤␤But yes, it's some “weirdo logic”, as you say. 😅
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@JacqBens @james_e_b_ Yes, that's a sensible way to say it, and probably more or less what I'd say (except for “in domain omega” where I'd just read “in omega”, or more probably “for any truth value q” because that's what it means in this case).
Just thinking out loud:␤␤j_φ(p) := “∀q:Ω. (((∃r₁,…,r_k:Ω. (φ(r₁,…,r_k) ⇒ q)) ⇒ q) ∧ (p ⇒ q) ⇒ q)”␤␤(where φ(r₁,…,r_k) is a propositional formula of k variables).
I asked on MathOverflow whether there is a known algorithm to draw a random preorder on {1,…,n} (i.e., sample the uniform distribution on such preorders). mathoverflow.net/q/491212/17064
Mood: the world is a weird and terrifying place, so let's eat and forget about it. x.com/SaarelaHC/stat…
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Updated version (I had misattributed one of the formulas — to Jankov instead of Plisko — and forgotten one — indeed due to Jankov — that is worth listing; so the table has one more line now): pic.x.com/pSf4jqoMQx
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Can you make something useful of such an oracle? Certainly: for a “needle-in-a-haystack” kind of problem, you can ask for a suggestion of where to look, and it has a non-negligible probability of being useful. But of course you can NEVER trust the answer, you must ALWAY check.
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Maybe imagine that for each topic you have a probability ~50% that the answers will be delivered by the benevolent genie and ~50% by the demon (who, of course, will try to make you believe he is the genie by giving answers that SEEM PLAUSIBLE when he knows you can't check).
I think the best way to approach asking a question to an AI engine and interpreting its answer, is to imagine you're asking the question to an oracle of which you do not know whether it will be answered by a benevolent and wise genie or a malicious demon trying to mislead you.
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On a more serious note, this collection of blog posts (by Bret Devereaux) about how ancient Spartan society was really like, and how the modern reimagining of it is utter fantasy, is well worth a read — I highly recommend them: acoup.blog/2019/08/16/col…
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Or as one might say in the emoji language of élite military planning:␤␤“👊🏳️‍🌈🔥”␤␤😆
Given how Spartan warriors are lionized by some not-too-savory bros (“μολὼν λαβέ”, etc.), I think it would behoove to occasionally remind ourselves how these supposedly invincible guys got their asses handed to them by a Theban band of ALL MALE LOVERS at Leuctra in 371BCE.
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@archimate In other words, the main point is that if two formulas do not have the same line of checks and crosses in the table at the start, then we know they cannot be used to prove one another [implicitly quantified universally over every propositional variable].
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@archimate The ones named “skvortsov” are taken from a paper by Skvortsov logicalinvestigations.ru/article/view/44 in which he uses them to separate the strength of a number of formulas. I extended the list by the simplest frames I could draw, and added some formulas distinguished by the whole set.
RT @JDHamkins: I answered a question of @gro_tsen on MathOverflow concerning whether there is an "Opposite" axiom to the continuum hypothes…
The Continuum Hypothesis tries to make the continuum as small as it can possibly be. But is there a natural hypothesis that tries to make it as large as possible? mathoverflow.net/q/491179/17064
RT @Jilcaesel: I have made an animated Gif just for you, @iamjohnoliver. pic.x.com/svODfY9uMj
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And the software used to generate it is here: github.com/Gro-Tsen/intui…
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The PDF file can be found here: gist.github.com/Gro-Tsen/f7631…
It took me an insane amount of effort to produce, but I can finally say I'm happy with this document showing the validity of various formulas of intuitionistic logic over various Kripke frames: happy both with how it looks and how it was generated. 😊 pic.x.com/HNBwQrevBw
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So, I think the best solution is this one: if $satcmdline is the value of the -e option, call "sh" with options "-c", "$satcmdline \"\$1\"", "sh", $filename. This allows arbitrary shell commands in $satcmdline but keeps $filename shell-safe! 💡 x.com/Jilcaesel/stat…
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@Jilcaesel github.com/Gro-Tsen/intui…
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@Jilcaesel Aaaaah! 😲💡 I hadn't understood your previous remark, and I didn't know one could do this.␤␤This is much better, thanks.
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… it also changed the description of the ‘-q’ option from “suppress all output” to “suppress most output”, because I guess that's what it's used to writing.␤␤So ⚠️ do not trust LLM output even when it is merely asked to convert something to something else. Check EVERYTHING.
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Project is here: github.com/Gro-Tsen/intui…␤␤It did a decent job, and I can say this was useful (I hate writing markdown and I never know what to say in these things), and it even made some useful suggestions for clarification (e.g., are loops and multiple edges allowed?).␤␤BUT …
I tried to use ChatGPT to write a (markdown) README file for me from a Perl program whose usage I had documented in the comments at the start of the file: chatgpt.com/share/67ff7b6d…
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@Jilcaesel So, just to be clear, your recommendation is to do something like this␤␤my $satcmdline = $cmdopts{e} // "cryptominisat --verb 0";␤open my $satsolver, "-|", "sh", "-c", "$satcmdline $outsatfile";␤␤?
I think I'd rather say this: in a debate between two persons, if either person changes their mind, they both win; and if neither changes their mind, they both lose.␤␤Debating isn't a zero-sum game! 😁 x.com/Jilcaesel/stat…
RT @Jilcaesel: Nobody can remember or keep note of the source for everything they know. Basic epistemic hygiene requires to remember the le…
RT @KyleKulinski: pic.x.com/l9LQBPT5wG
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Splitting at whitespace seems ugly because now we have the issue of what if the user wants to run a program with a space in the name, and I don't want to start having a quoting mechanism. Should I maybe have two options, one for the program and one for extra parameters for it?
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If the default command line were simply one program, I'd have a ‘-e’ option that takes a different program name, and let the user create a shell script if they want to use options. But here, the default already has options. Should I take a ‘-e’ option and split on whitespace?
Question on best practices:␤␤I'm writing a Unix (Perl) program that, by default, runs some command line (“cryptominisat --verb 0”, to solve a SAT problem). I'd like to allow the user to specify a different one.␤␤How should I do this in a way that is convenient for me and them?
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@An_07th Ça m'arrive de faire attention à écrire {u_0}^2, mais ça dépend vraiment des circonstances. Je n'ai pas de réponse universelle à ça.
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@ngspiensfr Généralement je les évite, mais pour un diagramme commutatif tu peux quand même difficilement ne pas le centrer.
Où j'explique en détails pourquoi je suis la convention typographique consistant à supprimer la ponctuation après une formule mathématique centrée, et quelle est sa logique: madore.org/~david/weblog/…
RT @SaarelaHC: Highland Cattle photo of the day pic.x.com/b58eKPi1gT
An incredibly thorough (but ultimately inconclusive) investigation into the question of why the IBM PC's graphical character set (“cp437”) and a character that looked like like ⌂ (small house? capital delta?) at position 0x7f: blog.glyphdrawing.club/why-is-there-a…
RT @rachid_yusuf: pic.x.com/hQDbvlteLt
Wisteria floribunda! pic.x.com/1aFnc494sN
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@Jilcaesel This is exactly my question.
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… an exception for this.)␤␤All this raises many questions. Why do we even need certificates that expire when the key hasn't changed? Whom are we trying to protect here, and from what, exactly? This isn't some banking web site, it has 0 confidential info — it's a WEBCOMIC. 😡
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… an exception, whereas this (right) is what I wanted to get by telling the browser “f🖕ck this security theater, I just want to read a webcomic, I don't care about its identity”. (The problem is that images and such are downloaded from a different host, and it's hard to set …
Since some people have tried to persuade me that HTTPS doesn't cause any annoyance in real life because even when a certificate goes wrong we can manually add an exception: one of my daily webcomic's certificate expired (left), and this (middle) is what I got when adding … pic.x.com/mxRzaFu8st
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Plus tôt dans l'après-midi: le lac des Deux Amants openstreetmap.org/?mlat=49.29251… pic.x.com/2Lb9iGKA7d
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Et quelques vues des Andelys et du château Gaillard depuis le niveau de la Seine: pic.x.com/3chNt3Hbxl
Vue vers les Andelys (Eure) et les coteaux de la Seine normande prise depuis le belvédère de la côte du Thuit openstreetmap.org/?mlat=49.25434… (on voit le château Gaillard à l'arrière-plan): pic.x.com/fOH8EQIuaM
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@garyniv I can't quite make out wherher this is the case on your photo, but sometimes you can see two different kinds of flowers on the same Prunus tree because the branches are typically grafted on the trunk and the trunk may decide to sprout its own branches and flowers. pic.x.com/I5zfIxHXUJ
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N'empêche que je crois que je préférais ces Prunus × yedoensis: x.com/gro_tsen/statu…
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L'an dernier: x.com/gro_tsen/statu…
Beaucoup de monde cet après-midi pour célébrer Hanami (花見) au bosquet nord du parc de Sceaux. openstreetmap.org/?mlat=48.76952… Si vous voulez y aller, c'est le moment! pic.x.com/lEL3GJ2TyY
RT @Geometriquement: C'est le problème de tous ces outils créés "pour la bonne cause" qui servent à contrôler les citoyens : on ne sait ni…
I finally asked a question that for decades I was too embarrassed to ask: what happens to the Ramanujan τ function (and the modular discriminant) if we replace the magical number 24 by some other number? math.stackexchange.com/q/5055524/84253
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Now reposted on MathOverflow: mathoverflow.net/q/490942/17064
I asked another question on MathOverflow today, about a sequence (𝐏_n) of properties of topological spaces defined by a condition on the intersection of closures, where (𝐏₂) is extremal disconnectedness, and each 𝐏_n is weaker than the previous ones: mathoverflow.net/q/490911/17064
RT @LeiboviciF: New tariff formula just dropped 👇 pic.x.com/HsVgc3Gt4C
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So it appears that the question is not as stupid as I feared it might be. But sadly, I suspect that if Emil Jeřábek doesn't know the answer, then nobody does.
In normal times, this would go without saying, but in the times we live in, even this tiny victory of the rule of Law, let alone by unanimous decision of SCotUS, is monumental. x.com/bykatiebuehler…
I asked a question on MathOverflow requesting a clarification as to the meaning of “completeness” when we say that topological semantics are complete for intuitionistic propositional calculus (because I've gotten myself very confused): mathoverflow.net/q/490891/17064
RT @NC_Renic: This is how tech people talk about AI pic.x.com/93z0hGeqL6
RT @phl43: lmao x.com/BillAckman/sta…
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I wrote a formula parser, and this is now starting to be potentially useful: pic.x.com/ZVUXOxBeZz
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Surtout que les règles bureaucratiques pénibles pour les fonctionnaires de base et les gens qui les fournissent sur les petites dépenses, je ne suis pas persuadé qu'elles évitent la corruption à haut niveau pour des dépenses de milliards d'euros décidées par le gouvernement. 🫤
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NB: Je ne dis pas qu'il faudrait supprimer toutes règles sur les marchés publics. Pour des gros marchés c'est évidemment souhaitable. Mais quand les procédures sont tellement pénibles qu'elles coûtent plus cher que l'objet acheté, elles sont nuisibles.
Le coût des règles bureaucratiques excessives sur les marchés publics en France: x.com/ngspiensfr/sta…
Starting to write a program that takes an intutionistic propositional formula and a Kripke frame and decides whether the formula holds in the frame by calling a SAT-solver. github.com/Gro-Tsen/intui…␤␤Core program done, now I need to write a parser (😒) and wrap-call the SAT-solver.
RT @SaarelaHC: Highland Cattle photo of the day pic.x.com/fq2X3CbehP
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@luca_defeo Be aware that there's a trend of usurpation of closed accounts (once the handle becomes available again). I would recommend either simply abandoning or locking the account.
I love the way the Web site “Kerodon” (kerodon.net) is illustrated with cute guinea pig drawings in a way that seems fitting for an elementary school textbook on mathematics… and then you realize it's about ∞-categories and homotopy theory. pic.x.com/8WQhrOGaIn
RT @ArmandDoma: the Chinese Communist Party posting Reagan speeches about the importance of free trade…what a time to be alive x.com/chineseembinus…
RT @haveigotnews: Boris Johnson has been bitten by an ostrich at a safari park. Medics were quick to the scene to carry out an emergency ch…
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I ✳︎think✳︎ the one on the left is Prunus × yedoensis (well, the grafted branches are), and the one on the right is P. serrulata (photographed 9 days later, so the leaves don't mean much). The difference doesn't exactly… leap to the eyes. pic.x.com/uSnhi0kRtU
How can one (phenotypically) differentiate Prunus serrulata from P. × yedoensis? (E g. the ‘Amanogawa’ cultivar of the former and the ‘Somei-yoshino’ cultivar of the latter.)␤␤Some seem to consider yedoensis a subspecies (variety?) of P. serrulata, I'm not sure.
RT @bearstech: Monster ! pic.x.com/MWG95aoqlS
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Source précise ici (“Les Misérables”, 5e partie, livre 2, chapitre 1 “La terre appauvrie par la mer”): fr.wikisource.org/wiki/Les_Mis%C…
«Paris jette par an vingt-cinq millions à l’eau. Et ceci sans métaphore. Comment, et de quelle façon? jour et nuit. […] Pourquoi faire? pour rien. Au moyen de quel organe? au moyen de son intestin. Quel est son intestin? c’est son égout.» (V. Hugo, “Les Misérables”, 5e partie) x.com/linstitutPR/st…
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@gine_robert Generally speaking, journal titles are always abbreviated when they are cited. But sometimes there is some confusion as to what the right abbreviation is (e.g., “Indag. Math.” = “Nederl. Akad. Wetensch. Proc. Ser. A” 🙄).␤␤When translating and transcribing, I don't know!
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@Dirque_L I don't know! (I mean, I agree that this is a reasonable abbreviation of the transcription of the name, but I don't know if this is what one is “supposed” to do.)
What is the most correct way to abbreviate the name of the journal ‘Доклады Академии Наук СССР’ (‘Proceedings of the USSR Academy of Sciences’) in Russian and in English?␤␤“Докл. Акад. Наук СССР” and “Proc. Acad. Sci. USSR”? Something else?
Many of us have in mind that Japan was a militaristic régime at the beginning of WW2, but how did it get there from the fairly democratic system it had in the 1920's? This interesting video summarizes what happens when the army takes control of the state: youtube.com/watch?v=voo0Cp…
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@GenevieveMadore Les délais de consultation des rhumatologues sont délirants. Il faut peut-être que j'en voie un à terme, mais dans l'immédiat, pour me faire prescrire du naproxène, je pare au plus pressé.
If only some great movie had been made about how working in a factory is so horrible it can drive anyone insane. pic.x.com/tN8dZ79qzF x.com/ariehkovler/st…
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Les jeunes: ne vieillissez pas, c'est vraiment pénible.
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Ce n'est pas la 1re fois que ça m'arrive, sans doute pas la pire, mais là je ne vois même pas d'élément déclencheur: hier matin ça allait bien, et ça s'est mis à faire mal au cours de la journée, sans aucun trauma.␤␤Je vais devoir supplier un médecin de me prescrire du naproxène.
Je me suis de nouveau fait une super tendinite à l'épaule droite (probablement calcifiante: un dépôt d'apatite qui se déplace ou se fragmente, causant une inflammation du tendon; j'en ai déjà eu). 🤒␤␤Je peux à peine lever le bras droit.
RT @Moinsdeuxcat: @gro_tsen Il m'est instantanément venu l'idée d'une fiction romantique mettant en jeu Hahn et Banach, tristement séparés…
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@Moinsdeuxcat Hahn-Banach 🇩🇰👊🇨🇭🔥
Useless trivia tidbit I learned yesterday: the highest point of Denmark (Møllehøj, 171m above sea level) is lower than the lowest point of Switzerland (Lake Maggiore, 193m above sea level). So Switzerland is ✳︎entirely✳︎ higher than Denmark.
RT @BallouxFrancois: I'm thrilled HHS is starting to engage with genuine threats to humanity. I hope they'll deal with space lizards next. x.com/DOGE__news/sta…
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@Jilcaesel OK, so… a double obsession with towers and holes. Dr. Freud would definitely like to have a word with Pr. Tolkien.
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@laurentbercot So sad to see you succumb to quackery. 🫥
RT @TheOnion: FBI Uncovers Al-Qaeda Plot To Just Sit Back And Enjoy Collapse Of United States␤theonion.com/fbi-uncovers-a…
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@LYMFHSR «␤Strong men create beautiful beef.␤Beautiful beef creates decadent men.␤Decadent men creates weak beef.␤Weak beef creates strong men.␤»
😬 pic.x.com/2KgdfLsnxX x.com/gro_tsen/statu…
RT @orthonormalist: DID I CRACK IT?␤␤I think I figured out at least a chunk of the math.␤␤It's trade deficit divided by their exports.␤␤EU:… x.com/RapidResponse4…
I presented a counterexample on MathOverflow showing that it is not true in general that, in a Hausdorff topological space, every non-empty open set contains a closed set with non-empty interior. mathoverflow.net/a/490409/17064
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@IanSolliec Not really, no. The intuitionistic implication A⇒B may be a tiny bit closer to the real-life intuitive idea of causal relation between A and B than the classical “B or not A”, but we routinely use the principle that something is either true or false, which intuitionism rejects.
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… ‘Let's Encrypt’ might be the good guys at this stage, but who knows whether they can be bought or taken over, and by whom? Something like half of the Web now depends on them, but who, exactly, operates it, and what are their bylaws?
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… The Web (and Internet) was made to be decentralized, but the certificate chain adds a strong centralizing element, so an element of potential control, and HTTPS makes this element mandatory. This is a centripetal transfer of power. …
Second unpopular opinion: the mania of requiring HTTPS everywhere has also created a huge opportunity for censoring the Web: blocking a Web site at the DNS or IP level is clumsy and can be worked around; but ordering CAs to refuse to issue certificates will be much more easy. … x.com/gro_tsen/statu…
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‣ In short: there is a homeostasis of overall security, but by putting HTTPS everywhere we are transferring security from places where it matters to places where it's just frivolous (e.g., Wikipedia), we are reducing useful security.
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… since HTTPS is now used in Web sites where “security” is meaningless or irrelevant; whereas previously HTTPS was only used on Web sites where there is, indeed, a meaningful risk of attack (e.g., banking sites) so one would take a broken certificate very seriously.
Unpopular opinion: ‘Let's Encrypt’ and the mania of putting HTTPS everywhere has, in fact, decreased the overall security of the Web, because users get used to encountering broken certificates and (rightly) instruct their browsers to accept them anyway, …
@GenevieveMadore Tu seras peut-être intéressée à lire ce joli hommage écrit (il y a trois semaines) par Nathalie Deruelle à Yvonne Choquet-Bruhat: ihes.fr/hommage-deruel…
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… “holds in intuitionistic logic because either ¬¬P is true, or if not, then (¬¬P ⇒ P) holds vacuously”: if you're going to write “or if not”, this means you're not doing intuitionistic logic, THAT'S THE WHOLE POINT.
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I'll give Grok a pass for not recognizing the formula as the “anti-Scott formula” because that is very very niche knowledge, or for not recognizing it as a formula in the Rieger-Nishimura lattice. But not only is the conclusion incorrect, the reasoning is laughable: …
Incidentally, I am not impressed by the supposedly superhuman AI's take on this formula (I asked out of curiosity): while ChatGPT just said something very boring and uninteresting but true, Grok3 claims, after minutes, that it is intuitionistically valid. It emphatically isn't! pic.x.com/WEhXbkLkwH x.com/gro_tsen/statu…
The more I think about the formula␤␤(((¬¬P⇒P) ⇒ (P∨¬P)) ⇒ (¬¬P∨¬P)) ⇒ (¬¬P ∨ (¬¬P⇒P))␤␤— the less I understand what it's trying to say.␤␤(This is in intuitionistic logic, of course. Classically, it's trivially true.)
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@JeanDellass Et si on perd grand max une demi-douzaine de politiques chaque année, ça me semble assez faible devant le vivier potentiel de qualité, et plutôt bon pour le turnover. Et à force les électeurs arrêteront de virer tout le monde.
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@JeanDellass Si chaque électeur ne peut signer la pétition, chaque année, pour soumettre au referendum d'ostracisme qu'une seule personne, ce sera dur de trouver assez de signataires pour faire plus qu'une poignée de referendums.
RT @phl43: It's kind of weird that music can affect people's mood and convey emotions when you think about it. Has anyone proposed a plausi…
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L'idée serait que toute personne qui cherche à faire de la politique autour de sa personne — plutôt que ses idées — finira forcément par subir la mesure. L'idée est aussi de purger les indéboulonnables de la politique, quel que soit leur camp politique.
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… si ce referendum donne un résultat positif, la personne est privée du droit de se présenter à toute élection à venir, ou d'exercer certaines fonctions (notamment, ministre), pendant qqch comme 5 ou 10 ans. (Les mandats en cours ne sont pas affectés.)
Plus j'y pense, plus je me dis que ce serait bien pour la santé des démocraties de rétablir une forme d'ostracisme. Du style:␤␤‣ Chaque année, chaque personne dont la proposition d'ostracisme a recueilli au moins N signatures font l'objet d'un referendum d'ostracisme: …
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Trump is an idiot, but he does understand the value of making threats when it comes to negotiating, and very often, a threat is stronger than the execution. ♔␤␤x.com/gro_tsen/statu… x.com/gro_tsen/statu…
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Also importantly, note that even if he doesn't do something he says he will do, the mere act of saying it is not innocuous (and not limited to shifting the Overton window).␤␤👉 Yes, he is serious about Canada, Greenland, etc.
There are two major mistakes one should avoid when thinking about Trump: ␤␤⁃ one is to believe that he will do what he says, ␤␤⁃ the other is to believe that he won't do what he says.
Et sinon, quelques vues de la Roche-Guyon cet après-midi: pic.x.com/UEETDk9ewR x.com/gro_tsen/statu…
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Le restaurant est plutôt cher (✻ au Michelin: il la mérite), mais le dimanche ils font un brunch sous forme de buffet, et c'est beaucoup plus abordable si on veut profiter de la vue.␤␤(Sinon, bien sûr, c'est un hôtel, mais j'imagine que les prix des chambres sont un peu salés.)
La vue du restaurant du “Domaine de la corniche” à Rolleboise (Yvelines) openstreetmap.org/?mlat=49.02259… est… plutôt pas mal.␤␤(Vers la gauche, le barrage de Méricourt. Au fond à gauche, Vétheuil. Devant, la boucle de Guernes et ses lacs. Au fond à droite, Limay.) pic.x.com/8qq8SPGdb1
I just noticed that if you search for “Prunus serrulata” in Google, there's a little easter egg. x.com/gro_tsen/statu…
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C'est peut-être la première fois que j'arrive à trouver des cerisiers aussi beaux que les pruniers-cerise de l'arboretum de Chèvreloup que j'avais photographiés aussi il y a quatre ans aussi: x.com/gro_tsen/statu…
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J'avais repéré ces cerisiers précis (route de Damiette à Gif-sur-Yvette) il y a quatre ans, et depuis j'avais cherché chaque année à les voir resplendissants au soleil, mais il n'y a que cette année que j'ai vraiment réussi. x.com/gro_tsen/statu…
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Les mêmes arbres ont été plantés dans le parking-relais de la gare de Courcelles-sur-Yvette (RER B), donnant à cet endroit banal une apparence complètement féérique (j'en ai rarement d'aussi beaux! — et à force, je m'y connais en cerisiers). openstreetmap.org/?mlat=48.70000… pic.x.com/bFujXUC54W
La ville de Gif-sur-Yvette a planté des cerisiers d'ornement 🌸 à fleurs blanches (Prunus × yedoensis je pense) le long de la route de Damiette, ils sont en fleurs en ce moment, et ils sont MAGNIFIQUES. 😍 Ça ressemble à du coton. openstreetmap.org/?mlat=48.69806… pic.x.com/uLSrKfLE2i
The future we were promised when I was a kid looked like this. ⬇️ What happened, where did we go wrong, and how do I get a refund? pic.x.com/4UqriROgUh
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I mean, this was supposed to be a silly joke: x.com/gro_tsen/statu…
What the f🤨ck is this even supposed to mean? x.com/amazingmap/sta…
RT @ishaantharoor: Missed this from last month — Dutch MEP @Gerbrandy trolled Trump with a video suggesting the Netherlands reclaim NYC␤␤ht…
Où je me lamente que l'Internet Archive n'arrive plus à archiver mon site Web, et que YouTube efface inexplicablement mon historique au bout de 46 jours: madore.org/~david/weblog/… (billet de blog pas interminable, pour une fois!)
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@antoineducros @VicP37508921 @Raywoaw @AdrienZabat @numbertheory0 Il faut vraiment inventer le concept de «sobriété mathématique» qui chercherait à ne pas construire des ensembles trop gros pour les quotienter juste après. Si ça se trouve ça peut même être intéressant à étudier!
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@VicP37508921 @antoineducros @Raywoaw @AdrienZabat (Si je ne m'abuse, partant d'un monoïde M, on fabrique tous les mots finis de la forme x₁ y₁⁻¹ x₂ y₂⁻¹ ⋯ et on quotiente par tout ce qu'il faut pour former un groupe. Donc pour former ℤ ce serait prendre toutes les expressions du genre 4−3+1−7.)
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@VicP37508921 @antoineducros @Raywoaw @AdrienZabat La complétion en question, c'est que le foncteur d'oubli de la catégorie des groupes vers la catégorie des monoïdes a un adjoint à gauche (qui envoie ℕ sur ℤ). math.stackexchange.com/a/605410/84253␤␤Mais la construction générale doit être encore moins économique.
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@VicP37508921 @antoineducros @Raywoaw @AdrienZabat @numbertheory0 À ce compte-là, si on construit ℂ comme ℝ[t]/(t²+1), on commence par construire un ℝ-espace vectoriel ℝ[t] de dimension infinie pour n'en garder qu'un quotient de dimension 2. C'est aussi assez peu «économique». 😁␤␤Les maths sont assez peu économes en général, en fait.
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@ngspiensfr And more importantly, the whole concept of the Book of Infinity is that it be copied again, and again, and again. 😁␤␤(I'm pretty sure I didn't invent the idea, anyway, except possibly in the minor respect of the URLs being stable.)
This “list of know anomalies in Unicode character names” (Unicode Technical Note #27) is a treasure-trove of geekery and pedanticism: unicode.org/notes/tn27/ I just love it! 🤩
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@stacycay Fact-checking this tweet: several independent calendars confirm that there have, in fact, been four September 11 days in every single presidential term, at least since the passing of the 20th amendment. 😏
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@TeamYouTube Thanks: I just sent you feedback per your instructions (if you need to find it, acct is “davidamadore” and first line says “My YouTube history auto-deletes itself after 46 days”). I attached the following screenshot that shows one more day of history gone w.r.t. previous tweet: pic.x.com/bLFLER4HVu
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@VicP37508921 @antoineducros @Raywoaw @AdrienZabat @numbertheory0 Je les copie-colle depuis une application de sélection de caractères (comme gucharmap sous Linux, ou UnicodePad sous Android, mais il y en a évidemment plein). Généralement je les trouve via leur nom Unicode que, à force, je connais très bien.␤␤Cf. madore.org/~david/weblog/…
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@TeamYouTube Following your advice, yesterday I tried signing out of YouTube on every device (I only use Web browers, no app) and then logging back on.␤␤It seems that this did not solve the problem, but I'll try again and check back in 24 hours to see if one more day of history vanished. pic.x.com/qgTUPX8xsp
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@antoineducros @VicP37508921 @Raywoaw @AdrienZabat @Thomas__Ga @numbertheory0 Spec ℤ aura le droit d'être une courbe quand on aura trouvé 𝔽₁ et qu'on saura calculer ℤ ⊗_{𝔽₁} ℤ.␤␤madore.org/~david/weblog/…
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@eliaschedid In a good way, j'espère! 😅
Of the very many things the Trump administration has done since January and I believe deserve blame for, I think the one that currently has everyone's attention should really be pretty far down the list.
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@ncfavier @JeanAbouSamra me l'a signalé sur le Good Place.
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@eliaschedid So apparently, it didn't work: the 2025-02-07 videos are now forgotten. ⬇️ I'm now trying logging out from every device and then logging back on, we'll see if that does anything. pic.x.com/5dWjIP9629
RT @TheOnion: Teen Warned Not To Accept Group Chat Invites From National Security Advisors She Doesn’t Know␤theonion.com/teen-warned-no…
RT @deepfates: pic.x.com/ebfRymOlDT x.com/deepfates/stat…
RT @ngspiensfr: Si le « Public Tech Fund » ne subventionne plus Let's Encrypt après le passage de Trump et Musk, il serait pertinent que l'…
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@zdimension_ That would be easy to do but it would sort of remove the magic of “any three cards have a symbol in common”, because the computer can very easily generate 3 such cards.
RT @buitengebieden: The dog has his own motorcycle.. 😎 pic.x.com/7zg8u8VJoM
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@eliaschedid One of the top comments on the latter says it's just a display issue, but in my case it's not: I downloaded the history from Google Takeout, and there's the same gap there.
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@eliaschedid I just did this. We'll see in a few days if it worked. Snapshotting this for now: pic.x.com/Ruk5oMcCAr
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@TeamYouTube Yes, confirming that absolutely ALL videos I watched, starting 2024-06-12, and up until “today minus 47 days”, are gone, from all devices, also from Google Takeout.␤␤And I double-checked that I have auto-delete history turned off.␤␤Acct is: youtube.com/@davidamadore
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@eliaschedid Yeah, it is super weird. It looks like an auto-delete feature that suddenly turned itself on, and there is indeed an auto-delete feature, but it has values like 3 months and 6 months, not 1½ month.
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@laurentbercot Je pense que c'est quand même moins vicieux si les symboles sont vraiment 130 trucs bien distincts, pas des combinaisons nombre+couleur. Là j'avais essayé (peut-être pas de façon très réussie, certes) de trouver 130 symboles qu'on ne risque pas trop de confondre.
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This is irritating, because I actually enjoy the YouTube recommendation algorithm, but now it's constantly re-recommending videos that have fallen into the gap, because it's forgotten that I watched them.␤␤(Yes, I'm actually complaining that Google doesn't know all about me! 😂)
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And these 46 days are shifting: on 2025-01-29 the gap of missing videos spanned between 2024-06-12 and 2024-12-13 inclusive, and now it's grown to span from 2024-06-12 to 2025-02-06.
For some reason, there's a large & growing gap in my YouTube watch history: it has the last 46 days (so now since 2025-02-07), as well as (seemingly all?) videos I watched up to 2024-06-11. But since 2024-06-12 it seems to retain only the last 46 days.␤␤Cc @TeamYouTube maybe?
Incidentally, I tried to find the one symbol common to the leftmost column in this arrangement, and it was really embarrassing how much time I wasted on this one simple mental task.␤␤(It's the letter ‘N’, if you want to know.) x.com/gro_tsen/statu…
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@Moinsdeuxcat Yes, I'm aware that the formula doesn't work! 😅
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I had the cards printed out by makeplayingcards.com and gave some copies of the set to a few friends, but I think I lost my own.␤␤Perhaps it would be nice to recreate this, but using a better set of 130 symbols.
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This is the 3-card analogue of a popular game called “Dobble”. Some explanations about how it was done mathematically (namely, using a Möbius geometry on the field with 5 elements) are on my blog: madore.org/~david/weblog/… (in French).
Some years ago I created this set of 26 cards (each showing 30 symbols out of a total repertoire of 130), which have the nice property that any 3 cards always have exactly 1 symbol in common.␤␤(So the game might be to draw 3 cards and see who can find the symbol first.) pic.x.com/o2o50lUwm5
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Bosch really deserves to be shamed all the way to hell for this.␤␤Please, people, if you buy a product that requires a smartphone app and/or Internet access for anything that is not strictly and obviously necessary (i.e., not rinsing dishes), give them disastrous reviews.
The absurdity of the modern Internet of Shit: Bosch made a dishwasher which, for many features (like… rinse cycle!), not only requires the use of a smartphone app, but also an Internet connection (and that the user sign up to a cloud account). jeffgeerling.com/blog/2025/i-wo…
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Also, for a long time, I was convinced that the length of an ellipse of semiaxes a,b had to be π·(a+b) (it's wrong!) because this works for a circle and it seemed that it “had to be” an elementary symmetric polynomial in a and b just like the area is π·a·b (this one is correct).
One thing which fascinated me when I was young is that there's no elementary closed-form expression for the length of an ellipse, BUT there is one for the area of an ellipsoid of revolution (aka “spheroid”). pic.x.com/kz5um2vQ1g
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With this measure, I seem to be about 44% famous on Twitter and about 41% famous on Bluesky. It's interesting that they turn out so close, suggesting that there is indeed something to this way of counting.
Your “celebrity score” (between 0 and 1, which can be converted to a percentage) on a social network shall be log(n)/log(N) (i.e., log_N(n)) where n = nb of followers including yourself, and N = number of users on the network.
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@Jilcaesel Je pense que tu es en train de te couper sur le rasoir de Hanlon. (Ou alors tu le sais et tu fais exprès.)
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@BallouxFrancois «The Signal App is known to have been compromised by the Russians. I wouldn't be surprised if the Chinese, and other State actors could listen in too.»␤␤Depending on what you're referring to, this is either a vast stretch of the word «compromised», or plainly false.
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@informatheux @Geometriquement Oui, non seulement il y a cinq tours dans le livre ‘Les Deux Tours’, mais une de ces cinq tours a une tour au sommet de la tour.␤␤Tolkien avait décidément payé sa cotisation au #ClubContexte.
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The morality seems to be that if you're called Thomas and you're a high ranking official under an English king Henry, try not to get in trouble with him.␤␤(Generally speaking, it is wise not to get in trouble with kings.)
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So, Thomas Becket was Lord Chancellor, got in trouble with King Henry II, and was murdered.␤␤Thomas More was Lord Chancellor, got in trouble with King Henry VIII, and was executed.␤␤Thomas Cromwell was chief minister of the same Henry VIII after More, and was also executed.
I realized that I was confusing Thomas Becket, Thomas More and Thomas Cromwell.␤␤(And worse than that, I was metaconfusing which two of the three I was confusing.)␤␤(And yes, Thomas Becket is ~350 years before the other two.)
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Also, was Tolkien aware of the existence of architectural forms other than towers? Or would Dr. Sigmund have something to say about this particular obsession of his? 🤔
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… And nobody knows which of the 5 are the eponymous “Two Towers”, not even Tolkien himself, who changed his mind several times about this: reddit.com/r/todayilearne…␤␤Why didn't he just name the book “The Five Towers”, then?
So, IIUC, the part of “The Lord of the Rings” that is called “The Two Towers” actually has (at least) FIVE towers prominently involved: Orthanc [Saruman's tower], Barad-Dûr [Sauron's tower], Minas Tirith [Gondor], Minas Morgul [Black Riders] and Cirith Ungol [orc tower]. …
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And no matter how much I hate these guys, I can't help find the fact that they use emojis like “👊🇺🇸🔥” to communicate between themselves… bizarrely endearing at some level.
I'm not going to comment on the “national security” aspect, but the fact that Trump's cabinet routinely uses Signal to communicate (like us plebs) is something I actually see as very interesting and positive. x.com/atrupar/status…
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@rapha_mil Exactly: x.com/gro_tsen/statu…
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I've said this before and I'll say this again: the most batshit conspiracy theories would often make great fictional material (and Umberto Eco would approve, I think).␤␤Like, Fomenko's crazy theories about history would make for a great setting for novels.
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This seems to be version 2 (or maybe they're rival claims, I won't pretend I understand): reddit.com/r/MapPorn/comm…
So #TIL that there's a flat earth theory version 3.0 or something, with lots of… interesting lands… beyond the ice walls. Also, three suns or something.␤␤(I have no idea who made this map, but it's AMAZING. 🤩) pic.x.com/ZLgyebgEKd
Some days I think that, if I were not such a stay-at-home person, I would mount a great expedition to reach the westernmost point on Earth, and, when I eventually get there, I would exclaim “see? they laughed at Columbus, too!”.␤␤Maybe it's best that I'm such a stay-at-home guy. x.com/gro_tsen/statu…
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@ngspiensfr @laurentbercot And I'm not saying this as a “gotcha”: I'm genuinely interested in any nuanced opinion about just any programming language you might have tried, where “nuanced” means you think it's not utterly great but also not utterly shit.
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@ngspiensfr @laurentbercot Your tweets x.com/ngspiensfr/sta… and x.com/ngspiensfr/sta… really do make it sound like you think only 4 languages are above “worthless”. But if I misunderstood your position, please feel free to correct it by suggesting intermediate tiers.
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2021 et 2022: x.com/gro_tsen/statu…
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2023: x.com/gro_tsen/statu…
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2024: x.com/gro_tsen/statu…
Fleurs de pommiers, saison 2025: pic.x.com/An48Fb4vAm
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@laurentbercot @ngspiensfr … My own appreciation of programming languages is that they're all mediocre at best (so, yeah, I'm picky too… maybe even more picky), BUT that some are less mediocre than others depending on the task at hand, and that they almost always have something to teach us.
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@laurentbercot @ngspiensfr … Whereas N.G. is picky because he has very strict ideas about what The Right Thing is, and apparently there's no level in between “adequate” and “irredeemable”. Which is perfectly his right, but not really informative for anyone who doesn't share his exact ideas about TRT. …
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@laurentbercot @ngspiensfr You two are picky for different reasons: you (L.B.) are picky because you want low-level control, and also because you care about system programming, you don't have to program stuff like a graphical user interface or mathematically complex structures. …
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@BallouxFrancois I'll just leave this here. 😉 x.com/gro_tsen/statu…
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@ngspiensfr For my part, I tend to apply the same criteria for programming languages as for online reviews (🔽): that is, I find most informative the opinions of people who have some good and some bad things to say about the language. x.com/gro_tsen/statu…
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@ngspiensfr On the other hand, the fact that (IIUC) you think every programming language in existence is shit except at most 3 or 4 (C, Perl, JavaScript, and… maybe OCaml I don't remember?) suggests that your criteria are… idiosyncratically stringent.
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“A developed country is not a place where the poor have cars. It’s where the rich use public transportation.” — Enrique Peñalosa (Mayor of Bogota, 2012)
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This makes me wonder: who are, currently, some of the richest, most powerful, most influential, most famous, or in any sense most “important”, people on Earth who regularly take public transportation with the plebs?
I learned through a Reddit post that Mark Carney used to ride the London Underground when he was director of the Bank of England.␤␤[And no, I know what you're all thinking, but he's not picking his nose!] pic.x.com/vJlMDiWact
RT @u_m_a_m_i: What makes you recognize someone are the near imperceptible differences in proportion, scale etc. You can't just apply "aver… x.com/topazlabs/stat…
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PS: If, like me, you have an account on both networks, I'd prefer our interactions take place as much as possible over there (if only for the fact that that other network easily lets me download and archive all my posts).
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If you can't figure out the name of that other network (which is made by concatenating the name of the color 🟦 and that of where the clouds are), try entering the part following the ‘@’ sign in the above image directly in your web browser's URL bar.
Periodic reminder of the fact that you can also follow me on another social network very similar to this one but with fewer trolls and with an open source code and an open API.␤␤I normally post the same things as here, but the discussion tends to be more interesting over there. pic.x.com/e8t1VPvgGI
Les magnolias de l'école Estienne (boulevard Auguste Blanqui, Paris), ce midi. pic.x.com/Vs08YSD65e
RT @mer__edith: GOOD MORNING AND GOOD NEWS!🌞 💐␤␤We are relieved to see the French National Assembly vote against the dangerous backdoor ame… x.com/mer__edith/sta…
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@calebstanford4 @JDHamkins … and now that we have a ranking of moves, we can re-evaluate the mistakes and say “oh well, maybe the mistake consists of making a non-optimal move but still the best among these”, and re-rank the moves according to that. I don't know where all this takes us!
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@calebstanford4 @JDHamkins The notion of allowing a player a very small probability of making a mistake is interesting, because we can start by saying they make a purely random mistake, but then we rank moves according to the probability of winning against an opponent who does this: …
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Et au passage, les notions de continuation-passing-style et de monade font une apparition un peu surprenante.
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J'avais déjà écrit ces définitions ici. 🔽 Le but du billet est, en gros, de prouver le théorème en écrivant du pseudocode pour faire la conversion. x.com/gro_tsen/statu…
J'ai écrit un billet de blog, s'adressant cette fois à des gens connaissant un peu de calculabilité, pour tenter d'expliquer une présentation alternative de la réduction de Turing et pourquoi elle m'intéresse: madore.org/~david/weblog/… pic.x.com/4F5GZWtqMb
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@laurentbercot (Of course, the truth is that even if the question were put to them we would not get an answer, or we would likely get very confused/contradictory/meaningless ones. But I'd still like to see a journalist press the question in those terms.)
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@laurentbercot Let's say I'm curious to know if they would go for the answer they really believe/want, and which would please their base (“only US citizens have any sort of rights”) or whether they care about trying to pretend not to spook everyone out of the country. This would be interesting.
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… Specifically, is criticism of president Trump considered sufficient cause for deportation of a legal resident? for imprisonment? etc. Whether the answer is “yes” or “no”, it would be nice to know. (And if the latter, advice must be given to foreigners not to enter the US.)
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… An answer such as «non-US citizens have {1st, 4th, 5th, 6th, 7th, 8th, 13th, 14th [due process]}-amendment rights» would be nice in my view, but even an explicit clarification that they have ZERO rights in the Administration's view is better than not knowing. …
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… (Of course, US courts already said a great many things on the question, see e.g. scholarship.law.georgetown.edu/cgi/viewconten… for a review. But the question is what the current US Administration thinks, and it doesn't seem exactly inclined to defer to the courts' opinion.) …
The US Administration really needs to be asked to answer clearly whether they think that non-US citizens have any rights whatsoever on US soil (and, if so, which rights), or whether they can be arbitrarily, e.g., deported, imprisoned, tortured, or enslaved. …
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Reconnaissons quand même une chose aux adeptes du sécuritarisme: le prétexte du «narcotrafic» était un tout petit peu original par rapport à leurs deux marottes habituelles qui sont le terrorisme et la pédophilie (pour passer n'importe quelle mesure liberticide). pic.x.com/BCY92HTA8T
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Bon, plein d'autres mesures liberticides sont quand même incluses dans cette loi, donc c'est une toute petite bonne nouvelle d'avoir un peu moins pire que ce qu'on pouvait craindre.␤␤Mais par les temps qui courent, on se contente de toutes les victoires qu'on a.
Petite bonne nouvelle dans un monde merdique: les tentatives du gvt français (surtout B. Retailleau) de se donner, prétextant la lutte contre le «narcotrafic», le droit d'espionner les messageries électroniques privées (Signal, Whatsapp, etc.) ont échoué à l'Assemblée nationale. x.com/reesmarc/statu…
RT @IsaacKing314: This is so cool. You can use 10 NAND gates to simulate a wire crossing, which means that any logic circuit in 3D space ca…
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@Moinsdeuxcat @ZenoRogue (I mean, the issue you point out should be solvable by standardizing the conditions in which the probabilities are measured, e.g., we let the same players play a large number of games so they learn to know how to best handle the other, and we assume they play to win.)
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@Moinsdeuxcat @ZenoRogue I think you're arguing a different point. My point was that Elo has an underlying assumption on how probabilities compose for three players. You're arguing that the probability doesn't even make much sense for two players. OK, but that's a different issue.
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On a more serious note, I learned this fact in this video (by the ‘Tribunate’ channel on YouTube) about the Third Punic War, and I thought it was very interesting: youtube.com/watch?v=fqjy3C…
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@ZenoRogue @JDHamkins As I like to point out, the Elo rating system has an interesting underlying transitivity assumption, namely that if Alice wins against Barbara with prob p and Barbara against Carol with prob q, then Alice wins against Carol with prob p·q/(1−p−q+2p·q). I wonder how true this is.
I like to joke that WW2 ended in 1990 because that's when the “two plus four” peace treaty was signed.␤␤But by that logic, there's even better: the Third Punic War ended… in 1985 CE. pic.x.com/tCQoV56Kp2
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@JDHamkins … maybe we can consider players who generally play optimally, but who have a small but nonzero probability of making a mistake (I can imagine several variants): then suddenly the notion of “slight advantage” might make sense even if optimal play leads to a draw.
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@JDHamkins I think we should see this as a limitation of the perspective provided by the notion of “optimal play”, and an invitation to seek other perspectives, in which a “slight advantage” might make sense. For example, …
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@laurentbercot x.com/gro_tsen/statu…
RT @PicturesFoIder: In 2017 Dr. Paul Locus was attending a Halloween party dressed as the Joker when he was urgently called to deliver a ba…
RT @investingidiocy: It's hilarious that one of the oldest known pieces of writing is from some poor guy in the back office of a Babylonia… x.com/Jbanklestankle…
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@VaeVix Non (enfin, il y en a un, mais il n'interdit qu'une poignée de pages et n'a pas changé récemment). De toute façon, la Wayback Machine ignore le robots.txt.
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The URL here is madore.org/~david/weblog/ and I really don't know why it would appear as “unreachable”.
The Internet Archive's Wayback Machine has once again decided that it thinks all(?) pages on my web site are “unreachable”. 😭␤␤I have no idea why this is so, and there seems to be no way to contact @internetarchive and no place to ask for help. pic.x.com/kH4oIl2Tjd x.com/gro_tsen/statu…
RT @clairlemon: I'm sorry but the world's wealthiest individual leveraging their wealth for political influence and power cannot claim vict…
I love it when the question starts “every mathematician knows Grunert's formula” and I don't know Grunert's formula. 😬␤␤(And, judging from the comments, I'm not the only one.)␤␤Nice formula, though!␤␤From: mathoverflow.net/q/488458/17064 pic.x.com/zNHJKfz51k
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@JacqBens You're right in that if we counted overlaps multiple times (which is arguably logical) then the total area would be infinite. But here the convention is to count them only once (and this is what makes the computation rather tedious).
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12823413011547414368862997525616691741041579688920794331363953564934456759066858494476606822552437442098640979 / 877512406035620068631903180662851572553488753575243048137500508983979170248733422547196905684808937723408093␤␤…fits in a tweet… but barely.
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Linked from: mathoverflow.net/a/489651/17064
I… did not expect a rational number with 108 digits in its reduced denominator to occur as the answer to the fairly natural question “what is the area of the Pythagoras tree fractal?”. penteract.github.io/pythagTree.html 😲 pic.x.com/5dC6yoDfQb
Bus en panne (ou coincé?) à l'angle des rues Saint-André-des-Arts et des Grands Augustins à Paris. Ils vont s'amuser pour le dégager de là! 😅 pic.x.com/hzLNnTyBiz
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@DoctorAnanas «dans le sens inverse» → Ah zut. Rien de pire que des conventions de sens contraire. 😖
I asked a question on Math StackExchange about whether we can state a Tonelli theorem for Riemann integration assuming all slices are R-integrable and the single integrals are (for the Lebesgue integral, this need not hold, as I recall in the question): math.stackexchange.com/q/5046993/84253
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@Geometriquement Oui, c'est tout à fait standard, et d'ailleurs l'existence du terme «clusivité» le montre.
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… comme il fait beau, on pourra manger sur la terrasse». Le «nous» (exclusif) fait référence au copain et moi, le «on» inclut le destinataire.␤␤C'est une distinction utile, surtout par SMS!␤␤Est-ce purement idiosyncratique, ou est-ce que d'autres gens font ça?
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… j'ai remarqué que (spontanément) j'ai tendance à faire évoluer le choix entre «nous» et «on» en une différence de clusivité, c'est-à-dire que j'utilise «nous» pour exclure le destinataire du message, et «on» pour l'inclure.␤␤P.ex.: «nous sommes partis, arrivons vers 13h. …
Une remarque sur l'utilisation des pronoms «nous» et «on» en français:␤␤J'utilise «nous» même dans des messages courts (genre SMS). Plusieurs personnes m'ont fait remarquer que c'est inhabituel. Mais il y a plus surprenant: …
RT @antoineducros: @gro_tsen Et je fais toujours le même commentaire sur le sujet : c'est très étonnant qu'aucun ouvrage ne soit revenu sér…
Un an après son écriture, et 5 ans après le premier confinement en France, je pense que ça vaut la peine que je refasse un lien vers ce billet de blog sur les leçons retrospectives de la pandémie: madore.org/~david/weblog/… x.com/gro_tsen/statu…
RT @StatisticUrban: "GPT o3-mini-high"␤␤"Gemini 2.0 Flash Experimental"␤␤"Grok 3beta"␤␤You bolt awake in the mountains of Carthage. You are…
RT @BallouxFrancois: “There is freedom of speech, but I cannot guarantee freedom after speech.”␤␤― Idi Amin
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@Moinsdeuxcat @tejotaefe Point taken. But you could write the same description (less 2-isomorphisms) for the points of a scheme, and in fact we know they form a set.
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@Moinsdeuxcat @tejotaefe What is it that worries you? That they may be too large to form a set? Geometers may have a tendency to look at fancy non-noetherian objects, but having more points than an inaccessible cardinal is rarely a serious preoccupation.␤␤The set of points is “coarse”, however.
RT @tejotaefe: how it started vs how it's going pic.x.com/838HpgWsam
RT @ichbinGisele: “Collectively, the AI search engines provided incorrect answers to more than 60% of queries.” ~ @CJR ␤␤🔗 https://t.co/57O…
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New source here: x.com/NateSilver538/…
An interesting general introduction to end-to-end encryption in general, the group encryption problem, and message layer security standard: vas3k.com/blog/end_to_en…
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@JacqBens And stretching a little bit the definition of a “biography”, Napoléon wrote a tale titled “Le Masque prophète” fr.wikisource.org/wiki/Le_Masque… which is the story of the heretic/prophet Hāšim ibn Ḥākim al-Muqannaʿ en.wikipedia.org/wiki/Al-Muqanna so we might call this a path of length four.
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@Bouhzigouloum There's an interesting n=3 case, at least: x.com/gro_tsen/statu…
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* Clarification: I meant to imply that X_0,…,X_n are distinct (otherwise any autobiography provides a path of arbitrary length with all X_i equal).␤␤The question of the existence of loops of length ≥2 is also interesting, though.
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@JacqBens Some very good and renowned authors have written biographies: as someone pointed out to me on the Blue Place, Stendhal wrote a biography of Napoléon, and Stefan Zweig wrote one of Stendhal, and Stefan Zweig has biographies of his own, so that's at least a length 3 path.
Silly morning question:␤␤‣ If “X→Y” (for X, Y two people) means “X wrote a biography of Y”, what is the longest known path for this relation?␤␤I.e., find people X_0,…,X_n, with n as large as possible, such that X_0 wrote a biography of X_1, and X_1 of X_2, etc., up to X_n.
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@Jilcaesel Penicillium camemberti and P. roqueforti?
Thou shalt never write the following phrase, followed by the same between quotes: “Thou shalt never write the following phrase, followed by the same between quotes:”
The more I think about this, the more embarrassing it gets. In classical math, or in constructive math with Countable Choice, “every real number is the limit of a sequence of nonzero reals” is a trivial exercise.␤␤But in constructive math without Choice, I'm stumped! x.com/gro_tsen/statu…
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@Moinsdeuxcat The obvious starting point would by my blog posts such as madore.org/~david/weblog/… — but I need to finish writing part 3 of that series first (which is about real numbers).
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@Moinsdeuxcat Writing a book about such things is, indeed, in my TODO-list.␤␤(It would rather be something like “constructive math”, because “constructive analysis” is more about, say, continuous functions & stuff like Bishop does — with Dependent Choice — while I would focus on reverse math.)
“‘I never thought leopards would eat MY face,’ sobs stock market which voted for the Leopards Eating People's Faces Party.” pic.x.com/ujmInCIztX
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So, it turns out that this club isn't so small: other examples provided here or there are (subject to interpretation of the question):␤⁃ Casimir Oyé-Mba,␤⁃ Alassane Ouattara,␤⁃ Charles Konan Banny,␤⁃ Anca Dragu (in reverse chronological order).
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Embarrassingly, though, I realize that I don't know whether one can prove (again, in constructive math without Choice) that every real number is the limit of a sequence of nonzero reals!
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I now posted an answer showing that one cannot prove (in constructive math without Choice) that every real number is the limit of a sequence of irrationals: in fact, βℝ∖ℝ provides a topological countermodel. mathoverflow.net/a/489193/17064
Mark Carney joins Mario Draghi in the very very niche club of “people who became head of government after having been head of a central bank, but not the central bank of the country of which they became head of government”.␤␤Are there any others?
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Mohammad Tahmasbizade's constructive math questions on MathOverflow are very interesting (if somewhat unorthodox), but I'm afraid they mostly highlight how little we know in constructive math without Choice.
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The question was whether we can prove in constructive math that every [Dedekind] real number is the limit of a sequence of negatively irrational numbers. But it's not hard to show that this fails for the positively irrationals, so this has led to some confusion.
I wrote an answer on MathOverflow which isn't really an answer to the question that was being asked, but which I hope will dispel the confusion between two different sorts of “irrationals” in constructive math: mathoverflow.net/a/489172/17064
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@galactiknavy @FiveThirtyEight 😬␤␤This makes my final question even more salient, then.
The link projects.fivethirtyeight.com/polls/approval… by @FiveThirtyEight which used to track Donald Trump's approval rating across various polls is now replaced by a generic redirect to ABC News' politics page.␤␤It still worked 2 days ago: web.archive.org/web/2025030702…␤␤Did the White House exert pressure?
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Links to the actual tweets: x.com/gro_tsen/statu… — x.com/gro_tsen/statu… — x.com/gro_tsen/statu… ⁂
Just to point out the absurdity of where we've arrived, here are three recent math tweets of mine that contain words from the Trump administration's scientific censorship list of banned keywords (namely: “intersection”, “bias” and “inequality”): pic.x.com/67KsbrIu4t
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@laurentbercot @_Matthieu_ Ben oui, pourquoi crois-tu qu'on parle de la Grèce «c'l'assique»? 😉
Ok, since several people have expressed surprise that I used the Attic dialect form of the word, “θάλαττα” and not “θάλασσα”, serious question:␤␤‣ How come is it that this word, one of the most widely recognized words in the Greek language, is so in its non-Attic form “θάλασσα”? x.com/gro_tsen/statu…
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@laurentbercot @_Matthieu_ … Je ne sais pas vraiment pourquoi pour ce mot précis la forme qui est passée dans le vocabulaire savant n'est pas la forme attique, alors que celui-ci est le dialecte grec considéré comme standard (notamment dans l'enseignement).
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@laurentbercot @_Matthieu_ Le tau se prononce/t/, pas de doute, mais dans le dialecte d'Athènes (l'attique) du grec ancien, «la mer» se dit «θάλαττα» (prononcé /tʰalatta/) et pas «θάλασσα» comme dans divers autres dialectes. Cf. en.wiktionary.org/wiki/%CE%B8%CE… et en.wikiquote.org/wiki/Sea …
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Dieppe pic.x.com/dE5qKdxhq4
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@_Matthieu_ Certainly not /vi/ like the modern Greeks do. 🧐
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@_Matthieu_ You were taught Ionic Greek. I was taught Attic. We are not the same. 🧐
Θάλαττα, θάλαττα! pic.x.com/uZxHS9oAWz
Quelqu'un peut-il m'ELI5 la différence entre «classé» et «inscrit» aux monuments historiques? (Et d'où sort cette terminologie idiote et confusante?)
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Encore trop tôt, on dirait! (Il y en a un qui a timidement commencé à fleurir, mais ce sera surtout pour la semaine prochaine.) pic.x.com/xSFsThZsZq
RT @publicsenat: Le patron des sénateurs Horizons, Claude Malhuret a vu sa violente charge prononcée contre Donald Trump et Elon Musk lors…
RT @BallouxFrancois: The chickens culled due to H5N1 exposure represent ~1.5% of all those slaughtered yearly in the US. There are sensible…
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pic.x.com/Vl4v1RPAHN
The semantics of combining emojis in Emoji Kitchen aren't super clear, but they do allow me to accurately express my current emotions at the current state of the world. pic.x.com/1KALosL4hv
A very insightful video on the recurring question of “when will I ever use <math concept>?” that students often ask, and why it's so hard to answer, but why this in no way implies that math is useless. (Applies more generally to many theoretical topics.) youtube.com/watch?v=RqQlXG…
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… For some inexplicable reason, it just received a sequel, 25 years later, still with Jeff Douglas. youtube.com/watch?v=_Ozbmr…
Remember that “I Am Canadian” ad for Molson beer that went viral in 2000 (and made Jeff Douglas rise to prominence)? … youtube.com/watch?v=WMxGVf…
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I would hope that US Congress cannot¹ enact legislation granting the President power to enact legislation. But now I'm not sure of anything any more.␤␤1. Unlike UK Parliament, which unquestionably can do this, even though it has a different status (“secondary legislation”).
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One underlying legal question is the extent to which an institutional body can delegate power granted to it by the Constitution (“does the power to do X imply the power to delegate the power to do X?”).
Regardless of whether they're opportune, isn't it a bit strange that even though the US Congress alone is supposed to have the power to raise (federal) taxes, but somehow the US President can still singlehandedly impose tariffs — which are taxes on imported goods and services?
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(Je suis allé les voir samedi, le 2025-03-01, mais c'était trop tôt. J'y retourne probablement ce week-end.)
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Depuis, j'attends chaque printemps avec impatience, et je photographie les prunus en fleurs (ainsi que les pommiers et d'autres), mais je n'ai jamais réussi à retrouver un instant aussi magique que ces arbres précis, le 6 mars 2021.␤␤Les mêmes en 2024: x.com/gro_tsen/statu…
Il y a tout juste 4 ans, j'ai photographié ces pruniers cerise (Prunus cerasifera v. divaricata) en fleurs à l'arboretum de Versailles-Chèvreloup openstreetmap.org/?mlat=48.82657…␤␤J'étais complètement émerveillé par leur aspect argenté, resplendissant au soleil. x.com/gro_tsen/statu…
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This theorem is not very difficult, but it's still tricky to grasp; its proof, and even statement, are hidden in the 1982 paper by Hyland “The Effective Topos” dpmms.cam.ac.uk/~jmeh1/Researc… , and I think it completely escaped attention, which is a shame. •4/4 x.com/gro_tsen/statu…
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… terminates and returns a P-answerer for B. And a “universal converter from B to A” is a g which is a P-converter from B to A for any P⊆ℕ (the same g for any P).␤␤‣ THEOREM: there is a universal converter from B to A iff A is Turing-reducible to B.␤␤•3/4
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… terminates and returns an (any) element of P.␤␤‣ A “P-answerer for A” is a program f which, if given ⟨m,e⟩ a P-querier for A, terminates and returns an element of P.␤␤‣ A “P-converter from B to A” (for A,B,P⊆ℕ) is a program g which, given f a P-answerer for B, …␤␤•2/4
I'll probably have more to say on this, but here is an interesting way to present Turing reduction:␤␤‣ If A⊆ℕ and P⊆ℕ, define a “P-querier for A” to be the code for a pair ⟨m,e⟩ with m∈ℕ and e is a program which, if given the Boolean value (1_A(m)) of “m∈A”, …␤␤•1/4
Ce n'est pas assez pour débarrasser cette propn de loi de tout ce qu'elle a de liberticide, mais c'est déjà un pas pour la rendre moins détestable. Remercions donc P. Molac, P.-A. Colombani et M. Froger d'avoir déposé cet amendement et protégé les communications sécurisées en 🇫🇷. x.com/reesmarc/statu…
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@Jilcaesel Le couscous, à l'origine, c'est bien la forme de semoule qui sert dans le plat, et c'est par métonymie que le terme sert pour désigner aussi le plat (i.e., le couscous stricto sensu accompagné de légumes et de viande).
Je n'arrive pas à décider si les gens qui ont créé une marque de vêtements appelée “+lelvetica” (pour contourner la propreté intellectuelle?), en l'écrivant de manière que tout le monde lise “Helvetica”, sont des génies ou des sagouins.
RT @ngspiensfr: Je viens de tomber sur ça au gré de la complétion d'« apt-get install geni<tab>so<tab> ». Quelqu'un connaît ? https://t.co/…
I asked a question on MathOverflow about whether the analytic WLLPO together with the sequential LLPO imply the analytic LLPO — which is also an excuse to write down what each of these terms mean. mathoverflow.net/q/488896/17064
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@ngspiensfr Clearly I don't have what it takes to be a YouTube celebrity + influencer + conspiracy theory peddler. 😐
Very disappointed that this particular conspiracy theory hasn't caught on. Now would be the perfect time for it to do so. x.com/gro_tsen/statu…
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Darn, this should be about continuous functions U→ℝ with U⊆X open rather than just X→ℝ. (For a completely regular space X this doesn't change anything because every germ of continuous ℝ-valued function at some x∈X extends to all of X.) I'll try to fix the question ASAP.
I asked a question on MathOverflow about topological spaces in which the positive and negative values of a continuous real-valued function always have disjoint closures, and a weaker form thereof: mathoverflow.net/q/488858/17064␤␤(The question relates to constructive math, but it isn't.)
RT @SaarelaHC: Highland Cattle photo of the day pic.x.com/wSO0BVM7se
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* Correction: interpretation #2 should read: “out of the four outcomes HH, HT, TH, TT, I told you that TT is excluded, leaving the other three equally likely. So the probability of HH, as asked, is 1/3.”␤␤(Accidentally adding confusion while trying to point out confusion. 😭)
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Both answers 1/2 and 1/3 are correct, it's just that the question isn't sufficiently precisely formulated to admit a unique definite interpretation (what does “one coin turned heads” mean? was the examined coin decided before the toss or did I search for a heads after the toss?).
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Interpretation #1: I told you that coin A turned heads, coin B is independent of it, so, 1/2.␤␤Interpretation #2: out of the four outcomes HH, HT, TH, TT, I told you that HH is excluded, leaving the other three equally likely. So the probability of TT, as asked, is 1/3.
How to cause endless discussions about probabilities by using insufficiently clear wording:␤«␤I toss two fair coins. I tell you that one coin turned heads. What is the probability that the other coin turned heads?␤»
Another intriguing constructive math question on MathOverflow: does␤␤∀x∈ℝ. ((∀r∈ℚ. ¬(x=r)) ⇒ (x≤0 ∨ x≥0))␤␤imply␤␤∀x∈ℝ. ((¬(x=0)) ⇒ (x≤0 ∨ x≥0))␤␤(where ‘ℝ’ is the Dedekind reals)?␤␤mathoverflow.net/q/488800/17064␤␤Of course, classically, this is all completely trivial.
RT @PalestraSociety: Isle of Skye, Scotland. pic.x.com/qGQrjp7JTx
I wonder if modern programming languages will ever reach the point when they're as good as Algol-68 was in 1968.
RT @EthanEvansVP: As a retired Amazon VP who experienced a 9082% increase in Amazon stock during my time, I am out of touch with many commo…
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@ngspiensfr @dsampaolo Les définitions ont l'air de vraiment partir dans tous les sens, il n'y a aucune cohérence entre les sources, parfois le même dictionnaire se contredit dans la même phrase: c'est vraiment le chaos!
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Si vous commentez, dites où vous avez grandi (ou où vous avez appris le français), parce que c'est fort plausible que le sens du mot varie d'une région à l'autre (voire d'une famille à l'autre).
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Le problème est que Wiktionary fr.wiktionary.org/wiki/petit-cou… définit «petit-cousin» dans le 1er sens (fils de cousin(e)), mais Wikipédia fr.wikipedia.org/wiki/Cousin_(f… le définit comme qqn ayant des arrière-arrière-grands-parents en commun, donc le 2e sens.
Question pour les francophones: pour vous, «petit-cousin» désigne:␤␤‣ Le fils d'un cousin ou d'une cousine? (Germain(e)?)␤␤‣ Un cousin plus éloigné qu'un cousin germain, mais de la même génération?␤␤‣ L'un ou l'autre, c'est ambigu?␤␤‣ Autre chose?
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@YannSkolan Oui, c'est-à-dire essentiellement négligeable, en effet.
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Source for the quote by DJT: x.com/TruthTrumpPost…
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Graph source: OurWorldInData ourworldindata.org/grapher/homici…
“So that we don’t end up like Europe!” 🤣 pic.x.com/FLOjhWfsGw x.com/MichalKubal/st…
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@Moinsdeuxcat It would appear so. I didn't give this any thought beyond “hic sunt leones”.
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@Moinsdeuxcat Aha! You mean you realize that the right object is not the set of real numbers but the locale of formal reals? You are a person of taste!
RT @gro_tsen: If only there were some way for a web site to store a small amount of information in a web browser that could be used to reme…
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@Moinsdeuxcat See: Burke, “Some remarks on density-continuous functions”, ‘Real Analysis Exchange’ 14 (1988–1989) 235–242 projecteuclid.org/journals/real-… (theorem 2).
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@Moinsdeuxcat One major problem is that if you put the density topology on ℝ on both sides (not just at the source), there exist functions f,g : ℝ→ℝ which are density-continuous but such that f+g isn't (we can even take g to be the identity). 😱 This is problematic for (f,g) : ℝ→ℝ².
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@Moinsdeuxcat Actually, even for ℝ², it's not quite clear what “the” density topology should be: see Horbaczewska, “On the density type topologies in higher dimensions”, Bull. Aust. Math. Soc. 83 (2011) 158–170 doi.org/10.1017/S00049…
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@GenevieveMadore Bon ben achète-le moi et tu me l'offriras à une occasion quelconque. 😁
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@Moinsdeuxcat «What is the most general setting where you can define it?»␤␤Aha! A Bourbakist has been unmasked! 😛␤␤(Seriously, I have no idea. Ciesielski &al define the “ℐ-density topology”, but I didn't even read the definition.)
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Previously: x.com/gro_tsen/statu…
Annoyed by the fact that Wikipedia didn't have an article on the density topology, I revived my Wikipedia account that had been dormant for 10 years, and created the page: en.wikipedia.org/wiki/Density_t…␤␤Not much there, but still better than nothing.
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(Je n'ai pas photographié la deuxième parce que les gardiens se tenaient à côté et je n'osais pas leur dire «pouvez-vous vous pousser un peu pour que je photographie la statue d'homme nu, svp?». Mais on la voit sur Google Street View: google.com/maps/@48.87858… .)
Les deux statues d'hommes nus qui gardent l'entrée du palais des sports sur l'île de Puteaux ont une esthétique qui mélange subtilement l'homoérotisme, le brutalisme de régime autoritaire, et l'esthétique art déco. pic.x.com/8v0qWa3tYz
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(C'est «de l'argent».)␤␤Ou peut-être que ce n'est pas parce que je suis vieux mais parce que, justement, dans la recherche, la moula, je ne risque pas d'en voir des masses, que je ne sais pas ce que c'est. 😬
Je suis officiellement vieux. Ma petite cousine (qui doit avoir environ 24 ans, et qui fait une thèse) m'a dit qu'elle voulait faire «de la moula» pour expliquer qu'elle ne voulait pas continuer dans la recherche, et je n'avais aucune idée ce que «la moula» signifiait.
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@NosCandidats Je crois comprendre que l'annonce est utilisée à la fois par les objets trouvés de la RATP et de la Préfecture de Police.
J'ai perdu mon bonnet ce matin, probablement dans le métro (il était dans ma poche et a dû tomber). Il n'a aucune valeur mais j'y tenais bien. Je me demande quelles sont mes chances de le revoir à partir d'une annonce de ce genre (sur le site des objets trouvés de la RATP). pic.x.com/jinQ26EHZ8
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@RogierBrussee (You mean “Ottonian”, not “Ottoman”, obviously.)
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… Also, I'm aware that they were both viewed, at the time, as being more or less identical to the Roman Empire, but my question is not how these empires were viewed at the time but as how they are viewed by later historians who study them.
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… but I'd like to know which is the more frequent classification used by modern historians, how and whether the point of view has changed over time, and what are the main arguments for considering the 800-founded and the 962-founded empires as different or identical. …
Is there consensus among historians as to whether the empire founded in 800 by Charlemagne is “the same” as the empire (re?)founded in 962 by Otto the Great and generally known as the “Holy Roman Empire”?␤␤This is more a classification problem than a historical question, …
RT @tomgauld: A cartoon for #worldbookday (coming on Thursday 6th) for this week’s @GuardianBooks. pic.x.com/7dSG4zY9x7
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@ISlovan Apparently not. ⬇️ But anyway, who in their right mind would ask a bullshit generator like an AI to check for the truth of something? They're sometimes useful for finding suggestions, but certainly not for this sort of tasks. pic.x.com/thpVTyAPFg
Cette citation circule en ce moment. Comme toutes les citations sur Internet, je m'en méfie énormément. Est-ce que quelqu'un peut vérifier si De Gaulle a vraiment dit ça, et, si c'est le cas, où, quand et dans quel contexte? (Merci de donner le livre, chapitre et numéro de page.) x.com/HistoiredeFran…
Things are really tense now, so here's a good old Dr. Seuss drawing from 1941 to lighten the mood (unedited): pic.x.com/t6wR1y4ciG
Going through my MathOverflow archive, I reran across this mindblowing little gem:␤␤There is a rational function of 2 variables f ∈ ℝ(x,y) that extends to a continuous function on ℝ², but which is not Lipschitz in any neighborhood of the origin! 🤯␤␤mathoverflow.net/a/436927/17064
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@laurentbercot … and those people who claimed that one was better than the other generally hadn't well studied the other, or were doing the religious vi-versus-emacs stuff all over again. But if you have in-depth knowledge, your expertise is one I would certainly give weight to.
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@laurentbercot PS: I don't know if you want to have this conversation, so don't feel pressured to have it. But so far, from what I understand of both ActivityPub and ATproto protocols, there isn't a clearly better one against hostile corporate takeover, …
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@laurentbercot The Fediverse is also going to become a billionaire network when Zuckerberg makes Threads interoperable with it. 😉␤␤But both AT and AP have serious anti-billionaire plans: AP's plan is at the server level, AT's plan is at the message/identity level. (And neither is perfect.)
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@laurentbercot Ah! That's a perfectly valid reason, I agree. I thought it was a matter of principle (which could also make sense, of course, but I was curious; both ATproto and ActivityPub made some interesting decentralization choices, even if they go in different directions).
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@laurentbercot Out of curiosity, what are your reasons for finding Twitter and the Fediverse acceptable places to post on, but not the ATmosphere?
RT @Kaimento: Can we have this button fucking everywhere x.com/vel_kia/status…
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@laurentbercot I didn't notice. But at this stage nothing would surprise me. And also, there's hardly anyone left for me to reply to on this site (most of my conversations take place on bluer skies) so Twitter gets very few replies from me anyway.
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@Sudetta9 You know, the whole point of an AI Large Language Model is to generate text that seems plausible, not true. Evidently given a difficult question, both “yes” and “no” are plausible answers, so it's not surprising they come up with both (and each with a plausible “justification”).
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Incidentally, one isn't supposed to use MO to check for the correctness of a proof, but I'd appreciate it if someone could confirm that the proof I wrote makes sense.
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The question contains a proof of the fact that changing the numbering gives a computably isomorphic algebra. Part of the question is why I've never seen this statement or proof anywhere.
I wrote a question on MathOverflow asking in what sense the first Kleene algebra (which is just ℕ endowed with a partial composition law given by application of partial computable functions) doesn't depend on the choice of numbering: mathoverflow.net/q/488585/17064
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I don't think the post-apocalyptic warlords will have tough looks and cool leather suits, though: given the sort of people who advise the US president, they're more likely to look like they can't control their hand nor their Nazi fetishism: youtube.com/watch?v=xzDghg…
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Also nothing disturbing at all about the richest man on Earth, who now also effectively runs the most powerful country on earth, telling everyone to prepare for the apocalypse.␤␤[Tweet id: 1895125730058785180] pic.x.com/UA6tgGSOrk
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(Is this parody? Perhaps it is. Who can tell at this point?)␤␤(Oh but, by the way, you can't say “ｃｉｓｇｅｎｄｅｒ” in the town square, because that's a slur and there is no place for such vile language.)
Perfectly normal conversation on a perfectly normal social media site. A real friendly town square where normal people chat about normal things. Nothing disturbing at all.␤␤[Tweet ids: 1894965364808917422, 1894969554540908958, 1894971117099680047.] pic.x.com/WpFp3TM2ku
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@laurentbercot … cercare e saper riconoscere chi e cosa, in mezzo all'inferno, non è inferno, e farlo durare, e dargli spazio.” (Italo Calvino, ‘Le città invisibili’)
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@laurentbercot … Il primo riesce facile a molti: accettare l'inferno e diventarne parte fino al punto di non vederlo più. Il secondo è rischioso ed esige attenzione e apprendimento continui: …
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@laurentbercot “L'inferno dei viventi non è qualcosa che sarà; se ce n'è uno, è quello che è già qui, l'inferno che abitiamo tutti i giorni, che formiamo stando insieme. Due modi ci sono per non soffrirne. …
RT @pbeyssac: La disposition anti chiffrement de la loi narcotrafic est une atteinte sans précédent au secret des correspondances en France… x.com/arnaud_thurude…
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This is the sort of shit which gives entire branches of math a bad name. If you write something like “by the Quetzalcoatl lemma” and you can't cite a book or paper where it's stated and proven, then giving the proof is your duty. Yes, it's annoying, but it's part of your job!
So apparently there's a lemma in algebraic homotopy theory or K-theory folkloricly known as the “Quetzalcoatl lemma” (probably bc it's a kind of higher “snake lemma”), but nobody bothered to write down a precise statement and reference: mathoverflow.net/q/488544/17064
Well, the United States was formed with France's help in order to screw the United Kingdom, that's the purpose of it. And now here we are. 🤷 x.com/atrupar/status…
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But I'm really impressed by how CSS systematically manages to make every simple task, no matter how trivial, annoying or impossible without JavaScript.␤␤“Reset property to default” should really be the most basic feature there is. HOW did they manage to miss this?
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See: quirksmode.org/blog/archives/…
Let me get this straight: CSS has a gazillion different reset keywords (“inherit”, “unset”, “revert”, “revert-layer” and “initial”) with super confusing meanings, but NONE of them does the ONE thing you want: “reset to the browser default for this element”?␤␤I HATE this standard.
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@Sudetta9 I tried asking it the fixed question (🔽) in “think” mode, and after ~3min thinking it gave me an answer that is not-entirely-wrong, but still very handwavy and not at all a mathematical proof. x.com/gro_tsen/statu…
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@Sudetta9 Except that I made a mistake in the question I wrote, and the answer is “trivially no” 🔽, so Grok3 is bullshitting you big time. 😅 x.com/gro_tsen/statu…
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Ah, I think this part of Barendregt's book ‘The Lambda Calculus: Its Syntax and Semantics’ (1984) answers my question. Apparently it's a 1978 theorem by Berry (“Séquentialité de l'évaluation formelle des λ-expressions”). pic.x.com/tHi8t43xfS
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‣ Does there exist a term T of the λ-calculus such that, given normal terms p,x,q,y, the term Tpxqy has a normal form iff px has a normal form or qy has a normal form [but no constraint on what Tpxqy should reduce to]?
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Never mind: if I take p,x,q,y to be variables, Tpxqy is supposed to β-reduce to either px or qy; assume the former w.l.o.g.: but then Tωωqy reduces to ωω (where ω := λz.zz), but also to qy; and by Church-Rosser, ωω should reduce to qy, which is absurd.␤␤So, weaker question: …
Une tentative (peut-être pas très réussie) dans mon blog pour vulgariser les bases de la calculabilité: madore.org/~david/weblog/…
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Possibly the question is completely idiotic, I'm not sure. If I have time to think about it some more, maybe I'll ask on something-or-other StackExchange.
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‣ Does there exist a term T of the λ-calculus such that, given normal terms p,x,q,y, the term Tpxqy has a normal form iff px has a normal form or qy has a normal form, and, if such is the case, β-reduces to one of these?
Standard fact in computability:␤␤‣ There exists a program T that, given p,x,q,y, terminates iff φ_p(x) terminates or if φ_q(y) terminates, and, if such is the case, returns one of these values.␤␤(Here, φ_n(z) := value at z of the n-th general recursive function.)␤␤Question: …
RT @Rainmaker1973: When the fandom has more creativity than the studios.␤pic.x.com/zDoAtl7WAu
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@ngspiensfr @Jilcaesel And do you know if trying to use the GPU to assist the encoding will be an inextricable mess or whether it's worth trying? (I don't even know where to start. I just know that the NanoPi has… some sort of GPU.)
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… Was I being utterly naïve here in expecting something like 5–10 times faster? Am I severely misjudging how many flops an ARM Cortex-A76 at 2.4GHz can crunch? Or is it that the libx265 encoder falls back to very slow generic code on ARM? Something else?␤␤@Jilcaesel maybe?
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… It re-encodes at roughly 0.04× of the original speed. Now I didn't expect real-time speed (1×), but I also didn't expect it to be THAT bad either. (I began to wonder if the CPU had an FPU: I checked, it does.)␤␤At this rate it would take ~7 months to re-encode my videos. 😱 …
I thought I'd re-encode some bulky car dashcam videos (~4000 each roughly ~230MB for 3min) as x265 using `ffmpeg -c:v libx265 -crf 30 -c:a copy` running on an ARM machine (NanoPi R6S: quad-core ARM Cortex-A76 at 2.4GHz + quad-core Cortex-A55 at 1.8GHz), and boy is it ❆SLOW❆. …
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… buy as standard academic practice: just like you don't need to ask for P's permission to use P's theorems, but you should still credit P and not claim the theorems as your own. (And here, AFAICT, I'm the first person to have computed images from ✷inside✷ a Kerr black hole.)
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… the image results from a mathematical computation with essentially no creativity involved, so there is no copyright — it is in the Public Domain — as all mathematical objects are; BUT that they should still credit me, not because of intellectual property laws, …
Every now and then I get an email from someone asking for permission to reuse one of the various mathematical images I computed, e.g., this ⬇️ image of the inside of a Kerr black hole (from madore.org/~david/math/ke…‌). And I have to explain that they don't need my permission: … pic.x.com/1KMk0E27mq
RT @Observer_ofyou: pic.x.com/Wzt2Y1usmf
I am not Catholic, nor a great fan of popes in general; but for all his flaws, I will say this about Francis:␤␤He seems to be taking the concept of “humility” seriously. And that's something we can all learn from, and I wish we'd see more in world leaders.␤␤So I hope he lives.
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@Jilcaesel OTOH, we've had “Mozilla plans to expand to <thing>” many times before (e.g., a mobile OS — which I even had on a phone!), and the only one which actually lasted and yielded something was Rust.
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@laurentbercot Yeah, well, it started in late 2019, so it's more like 5½, and things got really concerning about 5 years ago.␤␤(I'm well aware of this aspect of the passage of time because every week I re-read my personal diary from 1, 2, 3, 4 and 5 years ago.)
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Je rigole, mais je n'étais vraiment pas rassuré au moment d'aborder la montée de mon parking. Et en fait, non, aucun problème. Apparemment ça ne s'oublie pas si vite.
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Par exemple, je me suis immédiatement rappelé que l'espèce de barre horizontale devant moi servait à aller à gauche ou à droite (et que si on en tourne l'extrémité droite, ça va plus vite).
Bon, et sinon, aujourd'hui j'ai découvert que je savais encore conduire une moto.␤␤(Après trois mois sans y toucher pour cause de météo pourrie non-stop, c'était pas évident.)
Remember the good old days, four or five years ago, when we only had a global pandemic to worry about, rather than… <gestures wildly>… all that?
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(By “it is obvious that log(2)/log(3) is irrational”, I mean that even Pythagoras knew it… even though he didn't really know what irrational numbers where, and certainly didn't know what logarithms were. 🙃)
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Yes, it is also unknown whether e+π is rational, and whether e·π is (of course, they can't both be algebraic, so one of them must be irrational).␤␤But e and π are complicated: log(2)·log(3) should be more striking, given that it is OBVIOUS that log(2)/log(3) is irrational.
File under “we are embarrassingly ignorant of mathematics”: it is unknown whether log(2)·log(3) is rational: mathoverflow.net/a/488323/17064
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This seems to have attracted a number of perplexed comments. I agree there's probably no good answer to the question, but I don't think this fact is so obvious that the question shouldn't even be asked. 🫤
I asked a question on MathOverflow about whether we can characterize cardinals of the form λ^(ℵ₀) (they are ≥2^(ℵ₀) and of cofinality >ℵ₀ but this is not sufficient, so maybe something can be added): mathoverflow.net/q/488299/17064
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@Jilcaesel Non, pas la peine! 😅
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@Jilcaesel Je ne sais pas si la question t'intéresse encore un an après, mais le cas échéant la réponse est “oui” (je suis tombé dessus par hasard, ce n'était pas à l'endroit où j'aurais imaginé): pic.x.com/3faYTdQzVS
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Solved: βℝdens → βℝ can't be injective: it is surjective (as its image is closed and contains ℝ), so it would be a continuous bijection between compact spaces, hence a homeomorphism, so all bounded approximately continuous functions on ℝ would be continuous, which is false.
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@ngspiensfr Effectivement, je n'avais pas remarqué. Merci de la notif.
I am flabbergasted that I can't seem to find a reference for the fact that a semicontinuous function on a Baire topological space has a dense G_δ set of points of continuity. mathoverflow.net/q/488253/17064
RT @ngspiensfr: Diagramme de Venn pic.x.com/DxUU1JgafZ
I posted an answer to an old Math StackExchange question mostly as a pretext to draw attention to the notions of “normal lower semicontinuous” (and upper, of course) functions, a nice strengthening of lower semicontinuous functions that is better behaved: math.stackexchange.com/a/5037940/84253
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(The “density topology” on ℝ is the one whose open sets are the Lebesgue-measurable sets E whose points are all density points, i.e., which satisfy μ(E∩[x-h,x+h])/2h → 1 for all x∈E.) x.com/gro_tsen/statu…
Does anyone know this? Let ℝ be the real line with its usual topology, and ℝdens be the real line with the density topology, and let βℝ, βℝdens be their Stone-Čech compactifications. The identity map ℝdens → ℝ is continuous, so gives a map βℝdens → βℝ.␤␤Is it injective?
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@JacqBens I think my favorite one is the “admit lots of trivial new states to the Union and thereby pass any constitutional amendment” loophole.
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@JacqBens I don't have any theories of my own, but the paper by Guerra-Pujol, “Gödel's Loophole”, available at papers.ssrn.com/sol3/papers.cf…‌, suggests a few possibilities, and is fun to read.
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@JacqBens Since you liked my joke, you'll surely like this one as well: 😁 x.com/gro_tsen/statu…
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[Joke shamelessly adapted from bsky.app/profile/maitre… on the Good Place.]
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The solution turns out to be a simple generalization of a lemma previously proven by Richard Nixon (“when the president does it, that means that it is not illegal”).
Amazing! Very stable genius President Donald Trump solved a question that had been previously worked by the late great logician Kurt Gödel, but whose solution had been thought lost to time (and described as “one of the great unsolved problems”): en.wikipedia.org/wiki/G%C3%B6de… pic.x.com/U0PMqU1umV
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@JacqBens At least you'll note that I'm giving him the benefit of the doubt of having surrendered to the Russians rather than being their agent all along (as some on the left — wrongly I think — are inclined to believe). 😅␤␤Also, as a Frenchman, surrenders are my area of expertise.
So, 35 years after the US won the Cold War, 80 years after the Allies won WW2, and 160 years after the Yankees won the Civil War, it somehow took Trump only one month to surrender to the Confederates, the Nazis and the Russians.
RT @haveigotnews: Donald Trump claims that Ukraine started the war, just like all those American ships at Pearl Harbour that got in the way…
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(I'm not even sure MathOverflow is the best place for such a question. There's some discussing of related questions on quantumcomputing.stackexchange.com e.g., quantumcomputing.stackexchange.com/q/22064 — OTOH it's hard to argue that my question has anything to do with quantum mechanics, really.)
I asked a long and perhaps rambling, but I hope still interesting, question on MathOverflow, about one can do with certain magic communication devices that I call “p-trigadgets”, that are a kind of generalization of the Bell inequalities: mathoverflow.net/q/488138/17064
RT @gro_tsen: @CTorossian_Off Cette hésitation se retrouve aussi dans le fait que le français dit «féminité» là où l'anglais dit «femininit…
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@CTorossian_Off Cette hésitation se retrouve aussi dans le fait que le français dit «féminité» là où l'anglais dit «femininity». Mais «feminity» se retrouve (historiquement et/ou rarement) en anglais, et «fémininité» existe (dans un contexte/sens différent, mais proche) en français.
Interesting non-technical discussion on MathOverflow on how (non-technical!) journalists get their math stories or start talking about this or that breakthrough in math: mathoverflow.net/q/487989/17064
RT @informatheux: Nous, contributeurs et contributrices de Wikipédia, condamnons fermement les menaces faites à l'encontre d'un contributeu…
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(Oh wait, having co-authored a paper on the algorithmic computation of étale cohomology, maybe ✱I✱'m supposed to be one of the experts in which questions in algebraic geometry are effective. 😬 But of course I don't know. The “experts” are always other people.)
I asked a question on MathOverflow to which I suspect the answer is “the experts know this, but nothing has ever been written down”: “how effective (algorithmic) is the computation of the moduli space of algebraic curves of a certain genus?” mathoverflow.net/q/488062/17064
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@Jilcaesel @laurentbercot Relevant comic: existentialcomics.com/comic/590
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Like, at about 12 hours' distance:␤␤[tweet id: 1891492863789117509] pic.x.com/7lxWzOPUor
Let's check in with the self-proclaimed “free speech absolutist”, who as a side job likes to engage in deliberate deception to interfere with European elections (and rants that Europe has no free speech when told this is illegal).␤␤[tweet id: 1891310595397292169] pic.x.com/z4CPGbI8Bc
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I think the only sensible answer to this mess is: burn it with fire. Set LANG to “C.UTF-8”, which is the only sensible locale value, maybe set LC_MESSAGES, which is the only category which makes genuine sense, and configure everything else differently. •24/24
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Why can't “generation” of locales be done lazily as they're used? Why isn't it automatically done in the user's homedir if hasn't been generated by the admin? And also, why is it so INCREDIBLY SLOW (like, ~1s per locale: you don't want to generate all 500)? •23/24
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So you can't use, say, “LC_CTYPE=fr_FR.UTF-8” to refer to the UTF-8 encoding unless the system administrator has chosen to “generate” the “fr_FR.UTF-8” locale. Why does it need to be “generated”? What does this even mean? Why can't it infer UTF-8 from the “.UTF-8” suffix? •22/24
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But this is STILL NOT THE WORST PART. The worst part is that not only are there only a bizarre sets of possible locales, the ones which are actually available on a given system form a subset of that set, chosen by the sysadmin, over which you (as user) have no guarantee. •21/24
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(There is, however a “en_DK.UTF-8” locale, which oddly enough uses the ISO-8601 date format, so apparently someone considers that English is a language you can speak in Denmark but not in France. Again, nothing in this mess makes the slightest bit of sense.) •20/24
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But back to locales. Despite the purported orthogonality, not all language+country combinations are possible. For example, as a preferred English speaker in France, maybe I'd like to set all to “en_FR.UTF-8”, but someone (who???) decided there'd no “en_FR.UTF-8” locale. •19/24
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… Now I think the time zone selection mechanism (and keeping it out of locales!) is good. But that's my point: if you could do something like that for timezone, why not do something similar for every other “locale category” instead of tying them together artificially? •18/24
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Incidentally, before you say “well, at least the system has the advantage that we can set all categories to the same value through LANG”, consider there's sth very important that was left out of locales: time zones. They use a completely different mechanism altogether. … •17/24
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So, to summarize, we're setting each category from ctype to identification with a value that is composed of a language and a country, and sometimes also a charset, and various parts of this are extracted in a system that is supposed to be orthogonal, but really isn't. •16/24
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… whereas `LC_MESSAGES=zh_CN LC_CTYPE=en_US.UTF-8 touch /forbidden` does correctly give the Chinese error message encoded in UTF-8: so apparently, orthogonality between categories works in some cases but not in others. 🤷 I have no idea why, but the whole thing sucks. •15/24
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In any case, it doesn't even work as it should: if I run `LC_TIME=zh_CN LC_CTYPE=en_US.UTF-8 date +%x`, it's supposed to give me the date in Chinese (per “time” category) and encoded in UTF-8 (per “ctype” category), but it still outputs it encoded in GB2312, … •14/24
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… in which case it's absurd and wasteful to multiply locales thus, or there is one, in which case the ctype category does more than it's advertised to do. (Of course, nobody really knows, nobody knows who decides what goes in these locales anyway, or who appointed them.) •13/24
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So we have a “zh_CN” locale for Chinese with GB2312 encoding, a “zh_CN.GB18030” one for GB18030, and a “zh_CN.UTF-8” one for UTF-8. I have no idea what difference there is between setting LC_CTYPE to “zh_CN.UTF-8” or to “en_US.UTF-8”, but either there's none, … •12/24
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… that is in some arbitrary linked to the character set. This made no sense before Unicode came along, and it makes even less sense now that Unicode exists: so because of the ABSURD way locales work, every f😅cking locale had to be duplicated to a “.UTF-8” counterpart. •11/24
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The most absurd category, however, is the ctype one. So it's supposed to be a character set, and character sets have a standardized registry iana.org/assignments/ch… so it'd make sense to define it that way, BUT NO!, let's instead use a language+country combo … •10/24
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(Incidentally, I thought China used ISO-8601, but `LC_TIME=zh_CN.UTF-8 date +%x` gave me “2025年02月17日”, not “2025-02-17” like I wanted. Yes, I know I can use `date +%F` for this, but my question is which LC_TIME value I should set for all apps to use this format?) •9/24
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What the f🤪ck does it mean to set a paper size to “Austrian German”? This is ridiculous beyond words: so, if I want to use the international ISO-8601 standard for dates, I need to find some country (and, uh, language?) which uses it, and set LC_DATE to that? WTF? 🤦 •8/24
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This more or less makes sense for the “messages” category: setting LC_MESSAGES=de_AT means “please speak to me in Austrian German”, I can more or less understand. But the same designation system is used for ALL CATEGORIES. 🤯 •7/24
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But the way we specify each of these is by giving a code which consists of a LANGUAGE followed by a COUNTRY code. Something like “en_US” to mean “English as used in the United States” or “de_AT” to mean “German as spoken in Austria”. •6/24
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… measurement [units] and identification [???]. Maybe they vary from system to system, but that's the base list. And in each of these categories you can select a “locale”. So far this makes more or less sense: these are the things we want to customize. •5/24
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Anyway, back to the rant. How locales are supposed to work is that you have a certain number of categories, namely: ctype [=character type], numeric [format], time [format], collate [how to sort], monetary, messages, paper [size], name [?], address [?], telephone [?], … •4/24
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(As for languages, the setting I'd really like is “never translate”: in practice, this means “English” nearly 100% of the time, but it's not so much that I like English, it's that I have never seen a decent translation of any bit of computer software.) •3/24
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So first, just for context (not really relevant to the rant itself), I'd like my computer to use international standards whenever they exist. Date format, for example, should be YYYY-MM-DD because that is what ISO-8601 dictates. Measurements should be SI, etc. •2/24
The Unix/GNU/Linux system of “locales” used to configure things like numbers and time format, systems of units and the like, makes ABSOLUTELY NO SENSE.␤␤A rant. 🧵⤵️ •1/24
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@laurentbercot Oui, bien sûr, une fois le phénomène installé, il s'enracine. Mais dès le début j'étais plus à l'aise avec la moto, alors que j'avais quand même 1 an de permis B, parce que mes moniteurs de permis A2 m'ont très peu engueulé, contrairement à celui du permis B.
How the F🤬CK is one supposed to rename an mdadm array under Linux WITHOUT STOPPING THE ARRAY?␤␤You can hot-change the RAID level, number of devices and highly complex things like that, please don't tell me you can't change the LABEL without stopping the array.
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Et c'est même pas comme si je conduisais mal. Mais s'il y a un truc inattendu ou imprévu, je perds rapidement mes moyens à cause du stress, et du coup la possibilité qu'il y ait un imprévu me fait stresser, c'est un cercle vicieux.
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C'est complètement absurde et irrationnel: je ne suis pas stressé de conduire une moto, alors que c'est BEAUCOUP plus dangereux, mais dès que je suis au volant d'une voiture, c'est limite la panique. Et quand j'arrive, c'est vraiment un «ouf» de soulagement.
Ça fait maintenant 7 ans que j'ai le permis. Est-ce qu'un jour j'arriverai à atteindre le stade où conduire une voiture ne me stresse pas au point de me donner mal à la tête?␤␤Tout ça parce qu'on m'a trop engueulé pendant que je prenais des leçons de conduite, et ça persiste.
Start with the unit disk and repeatedly remove a disk of maximal radius for a given center. Assume the remainder is nowhere dense: need it have measure zero? I asked this on MathOverflow (in perhaps needlessly colorful language). mathoverflow.net/q/487959/17064
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@Marco_Piani @simulxxx And on the other hand, this part is also not at all bullshit: pic.x.com/eMqhTvA3h3
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@iconjack Well, there's no doubt that this is what's going on, is there?
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@simulxxx @Marco_Piani Well, several COBOL programmers have pointed out that this is a common practice. What, and it normalized by an ISO standard, so there's no doubt that this is what's going on in this particular case. What is your earlier quote from?
The outrage over “150-years old collecting Social Security” which turns out to be the way COBOL stores dates by counting dates from the 1875 Convention du Mètre (and represents missing values as a 0) is the exact metaphor we need for our age and time. 😬 x.com/toshiHQ/status…
RT @toshiHQ: It looks like Elon’s genius coders don’t know how COBOL works.␤␤Social security runs on COBOL, which does not use a date or ti… x.com/donaldjtrumpjr…
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@JDHamkins Not on the chart, but I also just realized that Évariste Galois could have met Lafayette. And not just in principle: had Galois not been kept out of the 1830 revolution, he would probably have been a major player, and so was Lafayette.
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@ngspiensfr Non, je n'ai pas écrit d'argumentaire propre. Tu peux renvoyer à madore.org/~david/weblog/… bien sûr, mais c'est plus un rant personnel qu'un plaidoyer.
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@atrupar x.com/gro_tsen/statu…
“It's a nice little business you've got going there, Canada: it'd be a shame if something were to happen to it. I think you need some protection. You don't have any protection. There are a lot of bad people out there. There's Russia, China. You're in danger, Canada, in danger.” pic.x.com/eXBusumRvq x.com/atrupar/status…
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@ngspiensfr Je pense que c'est le genre de mots qui existe dans le vocabulaire oral bien avant de percoler dans l'écrit et notamment dans l'écrit que Google Ngrams enregistre.
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Just to be clear, the Supreme Court is saying that criminalizing homelessness is fine because the law, in its majestic equality, forbids the rich¹ and the poor alike from sleeping in the parks.␤␤1. “Backpacker on vacation”. Yeah. Sure. Right.
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References:␤␤‣ Background on the ‘Grants Pass v. Johnson’ case: en.wikipedia.org/wiki/City_of_G…␤␤‣ Report and decision of the court: supremecourt.gov/opinions/23pdf… (excerpt is on p. 522)␤␤‣ Context of the quote by Anatole France: fr.wikisource.org/wiki/Le_Lys_ro…
🤨 SCotUS in ‘Grants Pass v. Johnson’ makes the EXACT ARGUMENT on criminalizing homelessness that was used as a joke by Anatole France:␤␤“The law, in its majestic equality, forbids the rich and poor alike to sleep under bridges, to beg in the streets, and to steal bread.” pic.x.com/vFAtwNoGRX
RT @NeilNevins: Yes, saying “hello” to common animals you see on your way to work like squirrels and pigeons makes you a better person. The…
RT @pbeyssac: Interdire, interdire, fliquer, interdire et fliquer. Et puis interdire. Et fliquer. La dystopie continue à (chercher à) se me… x.com/DarkJack999/st…
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Donc, si vous voulez me retrouver là-bas, mettez juste dans la barre d'adresse de votre navigateur le texte qui suit le ‘@’ dans la capture d'écran du tweet précédent.
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Oui, certes, cet autre réseau social n'a pas la killer-feature d'avoir à sa tête un milliardaire qui veut détruire l'humanité pour pouvoir se présenter comme son sauveur, mais je vous assure, on peut échanger des photos de chat et/ou parle de maths même sans ça.
Rappel périodique du fait que j'ai aussi un compte ⬇️ sur un autre réseau social dont l'interface est très semblable à celui-ci. J'y poste pour l'instant les mêmes choses qu'ici, mais les discussions qui s'ensuivent sont maintenant presque toujours plus intéressantes là-bas. pic.x.com/KUtNs8Rv15
J'apprends qu'elle est décédée aujourd'hui (à 101 ans, donc). x.com/gro_tsen/statu…
RT @lidlfrance: Nous rappelons aimablement que les combats de milliardaires ne sont pas autorisés dans nos magasins x.com/Xavier75/statu…
RT @NoContextBrits: pic.x.com/iRaOx45zut
I'd just like to point out that AI, as a research topic, is approximately 75 years old. academic.oup.com/mind/article/L…␤␤Anyone with newfound interest in AI should explain why they weren't interested decades ago, and why they started running thither just when all the lemmings did.
I asked a question on MathOverflow about how to construct a topos for realizability by Turing machines having access to a variable oracle that ranges over Baire space: mathoverflow.net/q/487603/17064
RT @gro_tsen: Gro-Tsen's third law of politics: for every stupid idea in politics there is an opposite and even more stupid idea.␤␤Gro-Tsen…
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@IanSolliec I don't understand it either: mathoverflow.net/q/438706/17064␤␤But the gist of predicativism is that mathematical objects can/should only be defined by reference to previously-defined objects (e.g.: don't define a subset of ℕ whose definition involves quantifying over subsets of ℕ).
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Diversity, equity and inclusion of mathematical philosophies is a good thing! ☺️🥰
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For the record, I find constructivism very interesting, and I too am fine with impredicativity. But I try not to preach any particular foundational choices in mathematics, nor to judge or berate my fellow mathematicians for their foundational preferences.
It is interesting to see a prominent constructive mathematician express regarding predicativism the exact thoughts that some classical mathematicians feel re constructive math and how ✵some people✵ preach it. mathoverflow.net/a/487510/17064 pic.x.com/ZlmZQqRazF
For no particular reason:␤␤“It is emphatically the province and duty of the judicial department to say what the law is.”␤␤— Chief Justice John Marshall, writing for the United States Supreme Court, in: Marbury v. Madison (1803)
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Note that the fact that you can use either the point or the comma as decimal separator is valid in any language. One may be preferred in this or that language, but the claim that, say, you must use the point in English or the comma in French has no normative basis.
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Source the for first point: ISO 31-0:1992/Amd.2:2005 standard cdn.standards.iteh.ai/samples/40910/… §3.3.2, and Resolution 10 of the 22nd CGPM bipm.org/en/committees/… — “the symbol for the decimal marker shall be either the point on the line or the comma on the line”.
PSA: there are international norms on how to write numbers. Please follow them:␤␤‣ “1,234” and “1.234” are BOTH equally valid ways to write 1234/1000.␤␤‣ The correct way to separate groups of digits is: “1 000 000”. Not “1,000,000” nor “1.000.000” nor “1'000'000” or whatever.
RT @SaarelaHC: Highland Cattle photo of the day pic.x.com/FcSTp8kd8F
Suggestion de recherche proposée par Google alors que je regardais un truc sur Louis XIV: 🤔 pic.x.com/xVcP7K9fsO
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And if you're asking what the Fourier transform of the zeta function on the critical axis is, good question!, and MathOverflow has you covered: mathoverflow.net/q/225327/17064
Music of the primes: this is the Riemann zeta function on the critical axis (i.e., ζ(½+i·t)) over imaginary parts 0 ≤ t ≤ 13 200, transformed into a 1min sound wave (left ear gets the real part, right ear gets the imaginary part).␤␤Plot of 0≤t≤60 purely for illustration. pic.x.com/7lZeVyPlNh
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@JacqBens (If you don't want to view another video by him, which I could quite well understand, then maybe just watch from 3′22″ through approximately 4′, when he defines what he considers to be “conservatism”, and, it seems, associates with.)
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@JacqBens Update: a few months later, the same guy posted a (much shorter) video explaining why he labels himself as “conservative”, what he thinks the word means and how he thinks it's evolving. It's not super deep, but I still thought it was interesting: youtube.com/watch?v=Rl8d8w…
For some reason, this story fascinates me. reddit.com/r/europe/comme… pic.x.com/yv19yaV58N
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C'est une version beaucoup plus développé de ce bref fil. 🔽 x.com/gro_tsen/statu… x.com/gro_tsen/statu…
Nouveau billet dans mon blog (avec des ✨illustrations✨) sur la théorie mathématique du marchandage selon Nash. Ou: comment négocier rationnellement sous une menace, et comment éviter de se faire la guerre. madore.org/~david/weblog/…
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Note also that the rate of warming may not be the same across the year. Here are two maps of Europe, generated with the same tool, the first showing the rate of warming in summer (June–August), the second showing the rate of warming in winter (December–February). Quite different! pic.x.com/FvG3VpzmpE
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@yiekshemash Je ne sais pas. Ça pourrait être, par exemple, que de la glace fond de l'Antarctique et refroidit l'eau de l'océan autour. Mais il n'y a pas forcément une explication qualitative simple.
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Note that places with small average warming rate as shown on this map can still be affected by climate change, as it can manifest itself on other meteorological variables, or as differences between seasons (e.g., warmer summers and colder winters can give a net zero warming).
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It was generated using the excellent “KNMI Climate Change Atlas” Web tool climexp.knmi.nl/plot_atlas_for… of the Dutch Royal Meteorological Institute. If you wish to reproduce it, use the following ⬇️ settings and click on “make map”. pic.x.com/BR9jZZZWu7
Climate change does not happen uniformly across the globe. Here ⬇️ is a map of the observed warming rate (linear regression slope of mean temperature) over the 1979–2025 interval. pic.x.com/IAlyTuSiPU
RT @_yesbut_: pic.x.com/SpCXzvVijo
RT @noampomsky: wait I love this pic.x.com/aLoyIQAZ2d
Letting the person with possible conflicts of interests determine whether there are conflicts of interests concerning them is the perfect solution to conflicts of interests: after all, they can't have conflicts of interests in that determination, or they would have determined. 😑 x.com/CityLab/status…
I just watched the movie ‘Aristotle and Dante Discover the Secrets of the Universe’ imdb.com/title/tt942874… and I absolutely loved it. It's super sweet, and all the actors are incredibly good at showing complex emotions.
RT @PR0GRAMMERHUM0R: imASerialOffenderToo redd.it/1ih2f04 pic.x.com/kRlYinINbF
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@JacqBens Effectivement, le mot français est «olfactif». Mais je n'avais même pas remarqué l'erreur, mon cerveau avait corrigé automatiquement. 😄
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Mais sérieusement, la question est: comment elle va interagir avec l'interfile des 2RM, cette mesure?
Les fabricants de poupées gonflables se frottent les mains. x.com/afpfr/status/1…
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@JacqBens J'ai effectivement un assez bon sens olfactif, et une bonne mémoire olfactive, et il m'arrive de croiser quelqu'un dans la rue et de me dire «mais je connais ce parfum, je fréquentais quelqu'un qui le portait… mais qui était-ce?», mais mettre le doigt dessus est très difficile!
Starting a trade war with Canada, Mexico, China, and, soon, the EU and the UK, seems like a super idea. 😔 x.com/amazingmap/sta…
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@MPapianne Pour les éditions III, VII, IX et XI je décrirais l'odeur comme un peu musquée. La VI est un peu musquée aussi mais également épicée. La IV et la X sentent plus frais. La V aussi, et légèrement fruitée. Mais tout ça est très subjectif!
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@MPapianne Ben il y a un parfum différent chaque année, justement (désolé, mon fil n'est sans doute pas super clair là-dessus). J'ai mis des liens vers quelques descriptions si j'ai pu trouver, mais comme c'est hyper difficile de décrire une odeur, je ne peux pas vraiment faire mieux.
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XI. Enfin, en 2024–2025, le dernier à jour, c'est «Goal». Pas de description en ligne, mais mon nez le trouve très proche du (IX). Je ne sais pas si les éditions (X) et (XI) sont sorties en version gel douche, moi je n'ai que les eaux de toilette. •19/19 pic.x.com/QlbphXiMQU
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X. En 2023–2024, c'est «Star» (oui, il y avait déjà eu une «Star Edition», la (II), mais là c'est «Star» tout court et le parfum n'a rien à voir). wikiparfum.com/fr/fragrances/… Parfum assez différent de tout ce qui est venu avant, je trouve, et que j'aime assez bien. •18/19 pic.x.com/stgvRtFsj6
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IX. En 2022–2023 c'est «Best of the Best» wikiparfum.com/fr/fragrances/… · fragrantica.fr/parfum/Adidas/… [ces deux descriptions sont un peu incohérentes 🤷]. Pour moi, elle évoque assez l'édition (VI), mais en plus réussie. •17/19 pic.x.com/IR5OwHdiQq
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Par ailleurs, je n'ai pas réussi à mettre la main sur la version eau de toilette. J'ai la version gel douche, dont j'aime bien l'odeur, mais je soupçonne que la version eau de toilette de cette édition n'a été vendue qu'en coffrets cadeau, contrairement aux autres. •16/19
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… donc «Adidas UEFA Champions League ‘Champions’», à ne pas confondre avec «Adidas UEFA Champions League ‘Champions Edition’» (la IV ci-dessus) ou «Adidas UEFA Champions League» tout court. C'est pas du tout confusant, tout ça! #ClubContexte (Parfois “VIII” est écrit.) •15/19
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VIII. En 2021–2022, Adidas a visiblement changé leur système et les eaux de toilette ont cessé de s'appeler «<Machintruc> Edition». Pour rendre les choses très confusantes, cette édition s'appelle juste «Champions» wikiparfum.com/fr/fragrances/… … •14/19
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VII. En 2020–2021 c'était le tour de «Anthem Edition». wikiparfum.com/fr/fragrances/… La version gel douche m'a beaucoup plu, mais la version eau de toilette sent un peu trop fort, je trouve (par ailleurs, il me semble qu'elle ressemble à la (III)). •13/19 pic.x.com/XQSvwqdude
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VI. Je suis un petit peu moins sûr de l'ordre, là, mais en 2019–2020 je crois qu'ils ont sorti «Dare Edition». wikiparfum.com/fr/fragrances/… · fragrantica.fr/parfum/Adidas/… Je trouve l'odeur un peu trop forte, au début j'étais déçu par cette édition, même si j'ai appris à apprécier. •12/19 pic.x.com/LWRM0T6EGw
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V. En 2018–2019, c'est au tour du «Victory Edition». wikiparfum.com/fr/fragrances/… · fragrantica.fr/parfum/Adidas/… Celui-ci et le précédent (IV) sont probablement mes préférés. •11/19 pic.x.com/g6qpkdBmrx
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IV. En 2017–2018, ils ont sorti «Champions Edition». J'ai trouvé qu'il était proche du (II) que j'aimais beaucoup, donc j'ai fait un stock. Difficile de trouver des infos en ligne dessus, parce qu'il y a déjà «Champions» dans tous les noms. 🙄 •10/19 pic.x.com/lEqMHrC7yg
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III. En 2016–2017, ils ont sorti «Arena Edition» (je ne vais pas réécrire «Adidas UEFA Champions League» à chaque fois). fragrantica.fr/parfum/Adidas/… Je l'ai acheté en pensant retrouver celui d'avant, mais c'était différent, et j'aimais moins. Il m'en reste un peu. ⬇️ •9/19 pic.x.com/o0Dc2kTM5s
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II. Ensuite, en 2015–2016, c'était «Adidas UEFA Champions League ‘Star Edition’». fragrantica.fr/parfum/Adidas/… C'est la première que j'aie testé, et j'aimais beaucoup, mais je ne savais pas que ça disparaîtrait et qu'il fallait faire un stock, donc je n'en ai plus. •8/19
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I. La première édition, donc, qui est sortie (je pense) en 2014–2015, s'appelait juste «Adidas UEFA Champions League». Je n'ai pas testé celle-là, mais il y en a une description ici: wikiparfum.com/fr/fragrances/… •7/19
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(NB2: J'ai essayé de reconstituer l'ordre des éditions à partir de souvenirs, des flacons que j'ai gardés, et de quelques traces que je trouve en ligne. Il est possible que j'aie commis des erreurs ou qu'il y ait des permutations, mais je pense que c'est à peu près bon.) •6/19
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(NB: Je me concentre sur les eaux de toilette. Adidas a aussi sorti des gels douches qui vont avec, de parfums proches, mais apparemment pas chaque année. Je n'ai pas enquêté de façon approfondie là-dessus.) •5/19
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Par ailleurs, je suis scandalisé qu'il n'y ait apparemment aucune page en ligne qui documente toutes les éditions successives de cette eau de toilette Adidas Champions League, alors le but de ce fil est de pallier ce manque. •4/19
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… et surtout que j'ai une certaine fascination pour “les choses qui viennent en séries variées mais avec un thème commun” (je n'arrive pas à expliquer exactement, mais j'espère qu'on comprend l'idée). Donc je les ai presque tous achetés et testés. •3/19 x.com/gro_tsen/statu…
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Voilà, chaque année depuis 2014 environ, Adidas sort une eau de toilette “UEFA Champions League”. Je n'ai aucun intérêt pour le foot, encore moins pour le foot de compétition, mais il se trouve que j'aime bien les parfums Adidas (gels douche, eaux de toilette, etc.), … •2/19
C'est parti pour le fil le plus inintéressant de l'Univers, où je vais vous parler des eaux de toilette Adidas Champions League. 🧵⤵️ (Sérieusement, vous ne voulez pas lire la suite, ça n'a vraiment aucun intérêt.) •1/19
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@anonymou5e_1 @fasc1nate “Florence, 1504. Palazzo vecchio. Two opposing walls, two painters: on my right, Leonardo da Vinci, on the left, Michelangelo. An apprentice: Raffaello. A manager: Niccolò Machiavelli. Forza Italia!”␤— Denis Arcand, ‘The Barbarian Invasions’ (2003) imdb.com/title/tt033813…
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@ngspiensfr Ah, je le connais celui-là, et moi aussi je ne lui parle pas.
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PS: I should add that ALL points with exact decimal coordinates on the unit circle are obtained from this 🔽 procedure + symmetries. This follows from the quantitative form of the two squares theorem, or, again, from prime factorization of 10^n in ℤ[i]. x.com/gro_tsen/statu…
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@JDHamkins Karl Marx, as a child, could (at least in principle) have met Thomas Jefferson!
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J'ai pris cette photo ⬇️ cet après-midi comme “preuve” de son inexistence, mais en fait ce n'est pas difficile de trouver des traces de sa suppression: cf. youtube.com/watch?v=AqM86x… par exemple. pic.x.com/8Qy6FbT9As
Le pont qui se trouve ici openstreetmap.org/?mlat=48.81335… (“pont de Prémol” à Dammartin-sur-Tigeaux, Seine-et-Marne, sur les voies de la ligne P du transilien) n'existe plus. Quelle est la procédure pour le supprimer de OpenStreetMap?
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@sflicht The line y=1/3 is birationally equivalent to the line y=0, but it has no exact decimal points. 😉
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(Incidentally, my name is David, I am Canadian, and I always rather liked that statue because… reasons.) pic.x.com/pNcnViNVtJ
“You're taking on Goliath” isn't quite the argument you seem to think it is when trying to warn the little guy not to take on the big guy.␤␤[tweet id: 1886013230931169315] pic.x.com/cHUHqotFYn
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@sflicht Which property exactly?
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This gives a sequence of points on the circle, which are exact decimals by the formulas for complex multiplication (or for cos and sin of a sum). Niven's theorem en.wikipedia.org/wiki/Niven%27s… shows that θ is irrational so they're all distinct (or argue by prime factorization in ℤ[i]).
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… But I think the nicest answer is to start with the point with coordinates (0.6, 0.8), which lies on the unit circle since 0.6²+0.8²=1, at angle θ := atan(8/6) if we want, and simply add θ again and again. (Equivalently, take the powers of the complex number z := 0.6+0.8·i.) pic.x.com/mDvuv2kTYZ
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Answer: there are various more-or-less equivalent answers here. The most complete answer is probably to appeal to Jacobi's two-squares theorem en.wikipedia.org/wiki/Sum_of_tw… in its quantitative form, but this sort of begs the question, and also doesn't explain how we find the points. …
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@ngspiensfr À peu près, oui. L'effet dépendra de la direction où elles éclairent (les lumens comptent un flux lumineux sommé sur toutes les directions), mais globalement tu peux ajouter.
“OpenAI Strikes Deal With US Government to Use Its AI for Nuclear Weapon Security” futurism.com/openai-signs-d…␤␤Not at all a concerning timeline. Nothing to worry about. All will be fine. Surely, SF authors would have warned us if giving AI control over nuclear weapons were bad.
@Jilcaesel bsky.app/profile/smooth…
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… and this new (ineffective) form quickly spread to the entire world, causing a shortage of the drug, with serious health consequences for patients. 😱
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… this could be a genuine practical concern in the pharmaceutical industry. 🤯 Apparently in 1998 the world pharmaceutical industry stopped being able to produce useable crystalline forms of the drug ritonavir because one plant started producing another form by accident, …
Disappearing polymorphs en.wikipedia.org/wiki/Disappear… are a crystalline form of a chemical compound that becomes impossible to produce once microscopic seeds of another, more stable, form are found in the environment. I knew this was a theoretical possibility, but I didn't think …
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@howie_hua “Adele” makes a fine first name (it already is one), and “Idele” might work too.
Why is it that Hebrew plurals seem to be overall regular (-im for masculine words and -ot for feminine ones) whereas Arabic plurals are formed by a seemingly completely random process of altering and/or lengthening vowels and reduplicating consonants?␤␤How was proto-semitic?
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@ncfavier Yeah, with that result alone they could very well all be of the form (5^k)² + 0² = 5^(2k) or (2×5^k)² + (5^k)² = 5^(2k+1), so you need a more quantitative result. (It turns out that Wikipedia has one, but you have to know where to look, and that's not really what I thought of.)
RT @pbeyssac: Nouvelle preuve, s'il en était encore besoin, que terrorisme, comme la protection de l'enfance, ne sont qu'un pied dans la po… x.com/reesmarc/statu…
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@letonyo @Jilcaesel Yeah, so it almost certainly had this exact problem in its training set.
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@Jilcaesel @letonyo Indeed. This is a consequence of Niven's theorem en.wikipedia.org/wiki/Niven%27s… but the AI (which I suppose had encountered the problem before, as it's probably a classic) failed to cite that, or some other argument (such as prime factorization in ℤ[i]).
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It is well-known that there are lots of points with rational coordinates on the unit circle: just pick any rational t, and ((1−t²)/(1+t²), 2t/(1+t²)) is such a point.␤␤But here we don't just want rational coordinates, we want exact decimal coordinates! How can we do this?
Another math puzzle: show that there are infinitely many points on the unit circle whose coordinates are exact decimal numbers (meaning, numbers of the form N/10^k for some k).␤␤For example: (0.6, 0.8) is such a point, as well as (0.28, 0.96) and (0.352, 0.936).
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@Conscrit_Neuneu Tiens, j'en ai profité pour revérifier: contrairement à ce que tu m'as prétendu, Éric Lombard n'est pas membre du Parti Socialiste, et pour autant que je voie n'a aucun lien avec, sauf d'avoir soutenu Michel Rocard il y a ~35 ans et de connaître Olivier Faure à titre personnel.
Taking the Greek word ΝΙΚΗ, transcribing it in the Latin alphabet as NIKE, then using Greek letters looking vaguely like those Letters to make it “look Greek”, resulting in ΠΙΚΣ, which just spells PIKS in Greek… this should be considered a crime against Humanity. 😖 x.com/kebabroyal_/st…
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@kebabroyal_ pic.x.com/PwXKTQGIk8
Following Donald Trump's lead, I'll now be blaming DEI hires whenever I fail to prove a theorem (indeed, the gay mathematician they hired to do my job fails to do my job, so it must be the hiring process's fault).
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(On second thought, these people probably wouldn't even care if all their documents were in Comic Sans. In fact, they probably are. Barbarians.)
Signs that I'm an insufferable nerd, episode #1729: seeing someone use the Cyrillic letter ‘Я’ in lieu of ‘R’, or ‘И’ for ‘N’, in order to somehow look Russian, makes me want to curse all their documents to be in Comic Sans forever.␤␤(These letters are VOWELS, you ignoramus.)
The real world has become indistinguishable from The Onion. whitehouse.gov/fact-sheets/20… pic.x.com/L8rtVv8pPX
RT @Dermatopoullos: La baisse du niveau scolaire peut avoir des conséquences dramatiques␤␤Je prescris colchicine 1/2 cp par jour ␤␤Quand je…
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@RogierBrussee (I can provide links, references or screenshots of various proofs if you want to know more. The proof given in Wikipedia doesn't quite prove the formulation I gave, through it's not far from it.)
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@RogierBrussee “E.g. a polynomial is well defined by its values but without a bound on its degree how do I know to stop asking the oracle for values?” → Exactly, that is what makes the theorem rather magical! (And it still seems so after reading the proof.)
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@ngspiensfr Obligatory xkcd: xkcd.com/783/
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Additionally, a transformation (F ↦ F′) from one to the other, i.e. converting from a program-that-can-inspect-e to a program-that-operates-on-a-black-box can ITSELF be performed algorithmically.␤␤Trying to write it down should make it clear that the theorem isn't obvious. •6/6
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In other words, “if you can compute something on all total computable functions g when given any program e that implements g, then you can compute that same something given just a black box that computes g (without access to e's code)”.␤␤And no, this is NOT obvious! •5/6
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THEN (says the K-L-S theorem): there is a program F′ that computes the same result as F, but instead of being given the code of e as input, it is given the possibility of interrogating a “black box” (or “oracle”) which, when given n, computes g(n). •4/6
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The second hypothesis means that if e₁ and e₂ are two programs that compute the SAME function g, then F must return the SAME result when given the input e₁ or e₂ (i.e. the result which F computes can depends only on g, not on how g is computed by e). •3/6
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⁃ provided that e terminates on every possible (say, integer) input, i.e., provided it computes a total function g:ℕ→ℕ, then F terminates on the input e; and␤␤⁃ the value returned by F on such an e depends ONLY on the function g that e computes (F is “extensional”).␤␤•2/6
There are several ways to state the Kreisel-Lacombe-Shoenfield theorem en.wikipedia.org/wiki/Rice%E2%8… but I think the following is most enlightening: 🧵⤵️␤␤‣ Imagine you have a program F which takes another program e as input and returns an integer (say). Also assume that: …␤␤•1/6
Quelques nouvelles en vrac (sur Bluesky/Twitter, mon cours de logique et fondements de l'informatique, la théorie de la négociation, l'hiver, etc.): madore.org/~david/weblog/…
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@ndemassieux I already posted the answer, but if you want to keep thinking, let's say I want a solution which works even if␤⁃ the loaded die is very very slightly off,␤⁃ or there isn't even a loaded die,␤⁃ or the loaded die is inconsistently loaded and its probability can vary with time.
RT @le_gorafi: Filmé en train d’envahir la Pologne, Elon Musk évoque un “geste maladroit” legorafi.fr/2025/01/28/fil…
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This property of having each possible value exactly one in each row and column is known as being a “Latin square” en.wikipedia.org/wiki/Latin_squ… — here we even have a “group law”, which is stronger.␤␤So no matter what the biased die says, the unbiased die ensures a uniform probability!
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ANSWER: the simplest solution is probably this: throw both dice at once, and take their sum modulo 6 (considering ‘6’ as being 0); or equivalently, take the sum and subtract 6 if it exceeds 6.␤␤This works because each number 1–6 appears once in each row and column in this table: pic.x.com/Gs6RV4V2PS
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@Sotorumuro We don't care what happens to cheaters: we care that if at least one player is honest, that player can ensure a fair throw by bringing a fair die to the protocol; so yes, it's equivalent.
RT @hausofdecline: These bots are becoming more sophisticated by the day pic.x.com/FPtb2woXPX
RT @tekbog: i cant believe ChatGPT lost its job to AI
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@Michael32376082 @b_subercaseaux I think I would rather say: like rolling the fair die, but randomly shifting its sides using the unfair one, which doesn't matter because they're all equally likely whatever the unfair one says.
Le concept des sites Web qui ferment la nuit, c'est vraiment 🤦😭 pic.x.com/7qrS0vnzI6
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@iconjack Much better. Although you might as well say (d₁+d₂)%6 + 1, or even “d₁+d₂ mod 6, and we agree that ⚅ means 0, which is indeed its value mod 6”. Or more generally: x.com/gro_tsen/statu…
@temptoetiam Tu n'as pas de compte sur le ciel bleu, par hasard? (À part une passerelle avec le mammouth.) Si tu t'en crées un, tu me feras signe, par mail ou autrement?
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@b_subercaseaux Another way to see it is to consider that Alice can completely control her die's outcome m (but only before she knows what Bob's fair die throw is): so we want a symmetric operation m⋆n so that for every m we just move around the n. Here we permute them cyclically.
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@b_subercaseaux One way to see it is to consider all 36 pairs of outcomes: you want to fill it with numbers 1 through 6 so that each line and column has one of each, i.e., a Latin square, because this will neutralize the biased probability distribution. Any group law on {1,…,6} will do.
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@EBrownien C'est marrant combien les gens tendent à trouver des solutions compliquées. 😅␤␤On peut faire avec un nombre de lancés borné a priori.
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@iconjack … So, can you fix ⓑ and ⓒ by sacrificing ⓐ (i.e., using both dice, and the assumption that one is fair)?
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@iconjack This works, but ⓐ it uses only one die, ⓑ on the other hand, it assumes that that die is “consistently loaded” so each toss has the same probability distribution, and ⓒ it uses possibly large (i.e., a priori unbounded) numbers of tosses. …
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Slight reformulation: Alice and Bob wish to throw a die to play a game; each brought a die of their own, but neither trusts the other's die. How do they do it?
Simple but instructive math puzzle: you are given two ordinary six-sided dice. One is fair (all sides are equally likely to come up), the other is loaded (some sides are more likely), but you don't know which is which. How can you simply get a fair throw using just these dice?
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… but what is its actual origin? I stumbled upon this interesting account of how the story was told and retold by different generations of storytellers, from the Babylonian ‘Talmud’ to Jean Cocteau and W. Somerset Maugham: subsublibrarian.com/2022/04/13/the…
Many people probably know this ⬇️ very short story, the “appointment with Death in Samarra”, as told by W. Somerset Maugham in his play ‘Sheppey’ (1933) and used as an epigraph in John O'Hara's novel ‘Appointment in Samarra’ (1934); … pic.x.com/Qg3r1eq1Ig
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This place is as close as you can get to zero criminality, it is the epicenter of political neutrality in the Universe, and they had no qualms about storing the (previous era) Nazis' gold.␤␤And you STILL managed to piss them off‽ 😂
So apparently the Tesla store in Zürich has been (very lightly) vandalized.␤␤Elon, do you realize how politically awful you have to be for your offices to be vandalized in ZÜRICH, SWITZERLAND? 😯 pic.x.com/JpksQulEL9
American AI companies are discovering that, when your product is a cheap and pretty useless gimmick to begin with, the cheap and shitty Chinese knockoff is going to be indistinguishable from the original product. x.com/KobeissiLetter…
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@laurentbercot “I may disagree with what you say, but I will fight to the death for your right to misattribute this quote.” (Voltaire)
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@laurentbercot Sorry, it appears that I'm repeating myself: x.com/gro_tsen/statu…
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@laurentbercot Sorry to disappoint you with another instance of “all the best quotes are apocryphal”, but the oft-repeated attribution of this maxim to Nimzowitsch is dubious at best, as this incredibly detailed investigation points out: chesshistory.com/winter/extra/n…
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@laurentbercot It's pretty much what Nash's theory says: that you should make threats of war, and be committed to following up on those threats, but in the end you don't need to go to war because there's a rational settlement which is better. (“A threat is stronger than its realization.”)
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Like: pic.x.com/igm5iSuCPn
This should be good news, were it not for the fact that public opinion has proven, time and again, that it is capable of having a completely different opinion about two obviously equivalent statements. And it's not difficult for leaders to pick a convenient formulation. x.com/USA_Polling/st…
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@laurentbercot The mathematical theory of genocide is even simpler:␤␤‣ Just don't do it.
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Ah oui, c'est bien un château d'eau, la carte IGN l'indique comme un réservoir, et on en trouve deux photos en cherchant «"château d'eau" "rue des Réservoirs" Chartres» dans Google Images: google.com/search?hl=fr&q… (peut-être «château d’eau des Perriers»).
Est-ce que quelqu'un sait quel est ce bâtiment bizarre situé à Chartres à l'angle de la rue des Réservoirs et de la rue des Comtesses, ici openstreetmap.org/?mlat=48.43751… sur OSM et visible ici google.com/maps/@48.43765… sur Google Street View. Une sorte de château d'eau, peut-être? pic.x.com/Uoh2Kfi4qS
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Namely, the rational outcome of the negotiation is the unique point of the Pareto-optimal boundary such that the tangent to the latter at this point has a slope negative of the line connecting it to the war point. (And thus was war forever ended by mathematicians. ☺️) •8/8
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So, given the (assumed known) convex region of feasibility and the (also known) outcome of war, what does Nash's theory of bargaining tell us that the rational outcome of the negotiation? Well, it turns out that it has an amazingly simple geometric description! •7/8
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(Note also that we can assume the region of feasible outcomes to be convex. Indeed, they can always agree that “with probability p we will do X and probability 1−p we will do Y”, realizing the segment between X and Y. Yes, this is highly theoretical.) •6/8
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(Note that both players are irrevocably committed to carrying out their threats if the negotiation fails, i.e., they will go to war even though war is clearly not the best outcome. But it is precisely this threat which ensures they reach a settlement!) •5/8
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… (in the sense that you can't improve BOTH player's utility). Now each player issues a threat of war to the other: if they can't come to an agreement, there will be (some kind of) war, whose outcome is represented by the red dot, obviously bad for both, and known to both. •4/8
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Two rational players (A and B) have to share some kind of resource, or come to some kind of agreement. The shaded area in the diagram represents the conceivable outcomes of the bargaining. Its edge are the Pareto-optimal ones, i.e., the ones which actually make sense … •3/8
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The detailed mathematical theory is presented in a 1953 paper by J. F. Nash, “Two-Person Cooperative Games”, available at jstor.org/stable/1906951 or neconomides.stern.nyu.edu/networks/phdco… — but let me very briefly summarize the main relevant conclusions. •2/8
This is arguably one of the most important mathematical diagrams for the real world (e.g., for geopolitics), because it tells us — in a highly simplified mathematical model — what the rational settlement out of a war is: ⬇️ (pardon my shitty figure). 🧵⤵️ •1/8 pic.x.com/LjDlP35Dck
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Update: version 135 beta is back to the previous interface (compare with screenshot in first tweet above). pic.x.com/tPsF1PQsz8
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@a_xel Dans le cas des vidéos YouTube, il y a une arme assez utile contre les titres putaclic, c'est summarize.tech — tu lui files le lien de la vidéo et il la résume en qqs lignes, ce qui permet de deputacliquifier le sujet et de décider si tu veux voir la vidéo.
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@GenevieveMadore C'est bien ce que je dis. Par contre, en hongrois, à la fois ‘ö’ et ‘ő’ existent; et le nom de Dénes Kőnig (contrairement au mot “König” en allemand) s'écrit avec ‘ő’.
RT @WholesomeMeme: pic.x.com/xjrQMY81I5
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PS: Previously: x.com/gro_tsen/statu…
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@JacqBens I'm going to ask some mathematician colleagues whether they saw it and how much sense it makes.
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The letter ‘ő’ is specific to Hungarian, it doesn't exist in German. You wouldn't want to confuse the guy on the left with the one on the right, would you? They have totally different… uh… tie knots. pic.x.com/cv5CXsycKh
No no no! I'm sorry, but even coming from Elon Musk this goes too far! It's intolerable! 🤬␤␤Hermann Göring's name spells with an umlaut: it's not “Gőring” with double acute, you dunce! Totally different.␤␤Now I have to do a grammar nazi salute.␤␤[tweet id: 1882406209187409976] pic.x.com/nAejQtKmzi
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… Mais je n'ai aucune idée de QUELLES informations complémentaires ils attendent de ma part, ni COMMENT leur transmettre des «instructions de livraison». Je n'ai reçu qu'un seul mail de leur part, celui disant que la livraison «n'a pas pu être effectuée». 🤷
Chronopost m'écrit que «la livraison de votre colis XXX n'a pas pu être effectuée ce jour dans votre point de retrait». Le site de suivi me dit: «Colis en attente d'informations complémentaires de votre part» et «Merci de nous transmettre vos instructions de livraison». … pic.x.com/ahdZYLFRJx
RT @Conseil_constit: Le Conseil constitutionnel est sur Bluesky. Rejoignez-nous :␤➡️ bsky.app/profile/consei… pic.x.com/aB0B15Z5bT
RT @ngspiensfr: Authentification sur le web sans javascript, le w3c consulte. Je fais circuler l'information, avant d'aller voir moi-même q…
This clearly doesn't go far enough: they clearly need to penalize just thinking about sex without actually having sex, because that is also a form of contraception, hence abortion, hence killing of sweet babies. x.com/TheTNHoller/st…
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@JDHamkins Phew! 😮‍💨 Ever since I learned that a subspace of a quotient is not necessarily a quotient of the obvious subspace x.com/gro_tsen/statu…‌, I've feared quotients in topology like the land of lawlessness and villainy. Maybe a tad too much, so!
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No, come on, I can prove that the quotient of X×{0,1} by the equivalence relation that identifies (p,0) with (p,1) is homeomorphic to X, it's pretty trivial. So what is the question asking about?
Am I misreading this MathOverflow question or is it claiming that not every topological space X is homeomorphic to the quotient of X×{0,1} by the equivalence relation that identifies (p,0) with (p,1) for every p∈X? Because this would BLOW MY MIND. 🤯 mathoverflow.net/q/486372/17064
RT @jimmy_wales: I think Elon is unhappy that Wikipedia is not for sale. I hope his campaign to defund us results in lots of donations fro… x.com/elonmusk/statu…
RT @TheOnion: Trump Claims He Can Overrule Constitution With Executive Order Because Of Little-Known ‘No One Will Stop Me’ Loophole␤https:/…
RT @tomgauld: A timely cartoon. Originally for @newscientist pic.x.com/ahGSvqIknf
RT @WallStreetMav: 🤣🤣🤣 pic.x.com/ELqRvYcFwG
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It is strategically wiser, if you hate him, to point out the many times where he's proved himself to be an idiot, contradicted his own promises and statements, shot himself in the foot, cheated, etc. Such things are unglamorous and expose him as the incompetent buffoon he is.
People talking about Musk's nazi salute are giving him exactly the food that the troll craves: worldwide attention, a smug sense of being a radical “independent thinker”, a plausible image of defending freedom of expression against censorship of political ideas, etc.
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@marklor @FPM_Paris L'archive des données fournies par Twitter est un minimum exigé par le RGPD (et probablement même pas assez, il manque, p.ex., les alt_text des images et les références des retweets). Le processus n'est en aucun cas automatisé. C'est utilisable une fois, pas de façon répétée.
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@marklor @FPM_Paris Ce n'est pas une API, hélas: les API publiques en lecture de Twitter ont été fermées par Musk, même pour récupérer ses propres tweets. Je le sais, parce que tiens à maintenir une archive publique de mes tweets madore.org/~david/tweets.… et c'est vraiment dur: x.com/gro_tsen/statu…
For no particular reason 😇, let me point out once again that this gesture ⬇️ is not a Roman salute, but that, from the painter David to its use by fascists and Hollywood moies it has a very interesting history that is worth reading about. pic.x.com/cyEfakdzIU x.com/gro_tsen/statu…
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I don't know if this specific takeover is hostile (i.e., Tommy Vennard's account was pirated) or friendly (i.e., he was persuaded to sell his account), but of course @/emiliechoiCbDev got insta-blocked from me.
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This is a common technique: take over an existing account so you get all their followers at once, who suddenly see ads for whatever the account is now about popping up in their feed from someone they follow, without knowing that they chose to follow a different person.
An example of account takeover on Twitter: user id 38185687, which used to be that of moto racing photographer Tommy Vennard (@/BigTommyGun) was taken over by a crypto scam under the name Emilie Choi (@/emiliechoiCbDev). Didn't even bother to clean the past timeline! pic.x.com/9GsLVtt5gL
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@JacqBens Thanks for cheering me up! pic.x.com/z4sbqv5oIk
Well, that's already five hours gone, and we've mostly survived. Only 35 059 left!
We're just minutes away from the End of the Universe, so where is the Restaurant?
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@conazole @VaeVix J'en ai même une sorte de confirmation expérimentale par le fait que je poste les mêmes choses sur Twitter et sur ⁧⁦y⁩⁦k⁩⁦s⁩⁦e⁩⁦u⁩⁦l⁩⁦B⁩⁩ et que le succès du même contenu sur les deux est… très mal corrélé pour dire le moins.
Je crois @Conscrit_Neuneu qu'il faut que tu te procures cet autocollant: reddit.com/r/europe/comme… pic.x.com/HcKfVLYk4p
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@GenevieveMadore @Conscrit_Neuneu Si, ça gelait aussi!
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@BallouxFrancois “You can no more win a war than you can win an earthquake.”␤— Jeannette Rankine (testifying before the Committee on Military Affairs of the US House of Representatives on 1935-01-29) pic.x.com/pYy1FKvDwZ
En général, @Conscrit_Neuneu et moi aimons profiter de nos week-ends pour nous balader en forêt, mais en ce moment, les forêts d'Île-de-France, elles ressemblent à ça ⬇️ donc c'est un peu bof. (Photos prises en forêt domaniale de Notre-Dame, vers Lésigny / la Queue-en-Brie. pic.x.com/JlxbiKegK1
RT @SaarelaHC: Highland Cattle photo of the day pic.x.com/0nyhpsSKZH
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@temptoetiam Comme je le signale dans le fil ci-dessous (qui doit être lisible sans compte), Mastodon et Bluesky ont tous les deux réagi au problème de la centralisation de Twitter mais de façon différente et avec des approches donc des limitations différentes: bsky.app/profile/did:pl…
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@gregeganSF This video, which I made some years ago, illustrates the same kind of hyperbolic displacement (a “translation”) in various different projections of the hyperbolic plane: youtube.com/watch?v=xHvAqD…
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1. “Some reason” is probably a strange combo of “EU regulations threaten exploitative business practices” and “still under apartheid SA's besieged racist mindset, so has weird fantasies about white ppl being endangered by immigration and perversely dreams of ‘saving’ them”.
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As a European I think I feel slightly less menaced by Trump, who doesn't care a bit about Europe and probably can't place it on a map, than by Musk, who for some reason¹ is utterly obsessed with destroying democracy in Europe. If only Americans hadn't elected Musk president!
This tweet is giving off the same energy as czar Alexander I of Russia at the Congress of Vienna explaining how he wants to make Poland great again. pic.x.com/AoG4aTQRjE
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@jeuasommenulle Maintenant que Météo France a ouvert plein de données, on doit pouvoir récupérer des données de stations urbaines ou péri-urbaines sur meteo.data.gouv.fr/datasets/donne… — mais le mécanisme que j'utilise ne permet pas du tout ça.
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@LavarenneT Oui, mais par inégalité triangulaire ça montre que ces stations sont extrêmement bien corrélées entre elles.
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@LavarenneT … donc savoir quelle mesure on prend pour faire ce genre de graphes n'a guère d'importance, du point de vue climatique et pour les températures la France est un ensemble suffisamment homogène pour ne pas nécessiter de discussion sur la nature exacte du modèle.
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@LavarenneT … parce qu'en fait les températures en un point de la France sont extrêmement bien corrélées avec les températures en un autre point: la température à Lyon n'est pas la même qu'à Paris, bien sûr, mais elle est en corrélation linéaire extrêmement bonne, …
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@LavarenneT … Et évidemment, on contrôle ensuite que le modèle est correct, p.ex., si on retire qqs points de données, il réussit à les reconstruire dans des marges d'erreur correctes. Mais s'agissant de la température en France, tout ça n'est pas vraiment important, …
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@LavarenneT … ça empêche que le modèle diverge de la réalité (comme ça se produit dès qu'on essaie de prédire la météo à plus que qqs jours), puisqu'on a des valeurs réelles tout autour. Le modèle utilise toutes les sources de données disponibles (stations, satellites, tout le reste). …
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@LavarenneT … Donc on prend toutes les données qu'on a, et on les utilise dans un modèle météo analogue à ceux utilisés pour faire des prédictions pour l'avenir, mais la différence essentielle est qu'ici on fait de l'interpolation et pas de l'extrapolation: …
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@LavarenneT Le but de la réanalyse ERA5 est de reconstruire (approximativement, bien sûr) les paramètres météo en n'importe quel point de la Terre et du temps, alors qu'on n'a des mesures qu'en certains points de l'espace (stations météo) ou du temps. …
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An interesting case study is the history of the notion of equivalence in mathematics (which we now consider equivalent to the notion of “equivalence relation”, but things are more complicated): x.com/gro_tsen/statu…
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… So asking “who was the first to discover/invent <X>?” may have a very different answer according to exactly what you consider to represent the idea <X> (a very small — and now unimportant — change in formulation can yield a completely different answer). …
One recurring problem in the history of science (or more generally, the history of ideas) is that two ideas that we now consider “obviously equivalent” may not at all have been “obviously equivalent” at the time. …
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@LavarenneT J'avais fait ces scatterplots entre la température moyenne en France donnée par ERA5 et celle donnée par différentes stations météo, et la corrélation est vraiment excellente: x.com/gro_tsen/statu…
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@Gauvain_georges (Je parle juste du premier graphe du tweet cité. Le printemps y est en vert, l'automne en violet.)
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@Gauvain_georges Notons que c'est “printemps” comme mars-avril-mai et “automne” comme septembre-octobre-novembre (saisons météo et non astronomiques). Les graphes suivants aident peut-être mieux à voir: x.com/gro_tsen/statu…
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@LavarenneT La réanalyse ERA5 reconstruit la température sur l'ensemble du globe à partir de toutes sortes de données (relevés de stations, mais aussi mesures satellites, calculs, etc.). Donc ce n'est pas biaisé par le changement du nombre de stations (qui, en France, est assez stable).
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Et je me dois d'insister, parce que le grand public a parfois du mal avec la différence: ce sont là des OBSERVATIONS sur 1950–2024, pas des PRÉDICTIONS ni un modèle pour l'avenir. ❧ Je refais ce fil de temps en temps; version précédente: x.com/gro_tsen/statu… •15/15
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Revoici les pentes des régressions, i.e., l'ampleur du réchauffement observé, et aussi l'incertitude statistique dessus (pas sur le graphique):␤‣ hiver: +(2.64±0.65)°/siècle␤‣ printemps: +(2.49±0.46)°/siècle␤‣ été: +(3.30±0.48)°/siècle␤‣ automne: +(2.24±0.43)°/siècle␤•14/15
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Je devrais peut-être donner les coefficients de corrélation (r de Pearson) de ces régressions: ils nous indiquent quelle partie de la variabilité saisonnière est expliqué par la tendance séculaire trouvée:␤‣ hiver: 43%␤‣ printemps: 53%␤‣ été: 63%␤‣ automne: 52%␤•13/15
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… ce qui fournira un .zip contenant les données qui (contrairement au graphique affiché) remontent à 1950 (attention, dans le fichier les années sont numérotées par le début de la saison, contrairement au graphique!). Ce sont ces fichiers que mon code Gnuplot utilise. •12/15
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… il faut aller sur cette page et utiliser les réglages suivants (pour l'hiver, et ajuster le mois de départ pour les autres saisons), puis faire “make time series”, ignorer le graphique (qui ne commence qu'à 1979) mais cliquer sur “all data” en petits caractères … •11/15 pic.x.com/iWIRDwPRYj
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Les données elles-mêmes proviennent du KNMI Climate Explorer & Climate Change Atlas climexp.knmi.nl/plot_atlas_for… et sont des moyennes calculées sur la France des valeurs de la réanalyse ERA5. Voici la procédure exacte pour les récupérer: … •10/15
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Si vous voulez le reproduire, le code Gnuplot ayant servi à faire ce graphe est le suivant: gist.github.com/Gro-Tsen/4d90c… (les fichiers `time_era5_t2m_France_metropolitan_mon12_ave3_dump0.txt` et compagnie sont à télécharger sur l'Atlas of Climate Change comme décrit ci-après). •9/15
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(Pour être ultra précis, la saison qui commence au mois numéroté m de l'année y est placée à l'abscisse y+m/12 dans le graphique. Donc par exemple l'hiver de décembre 1962 à fin février 1963 est à l'abscisse 1962, et c'est ce paramètre qui sert en entrée des régressions.) •8/15
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Voici la lecture de la légende pour accessibilité:␤‣ hiver: régr. 4.35° + 2.64×(Y−2000)/100 ; σ=1.19␤‣ printemps: régr. 10.32° + 2.49×(Y−2000)/100 ; σ=0.85␤‣ été: régr. 18.63° + 3.30×(Y−2000)/100 ; σ=0.88␤‣ automne: régr. 11.80° + 2.24×(Y−2000)/100 ; σ=0.79␤•7/15
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… il reste toujours des points très hauts ou très bas. Il est donc parfaitement impossible de conclure quoi que ce soit d'intéressant à partir d'une année particulière: il faut regarder une tendance à long terme pour que le phénomène soit évident. •6/15
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C'est peut-être ce fait qui rend la compréhension du réchauffement climatique difficile au grand public: les variations aléatoires d'année en année restent très importantes, même après moyennage sur 3 mois, donc même si la pente séculaire est parfaitement claire, … •5/15
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La bande de couleur est la bande, centrée sur la droite de régression, dont la demi-largeur est donnée par un écart-type résiduel (dont la valeur est donnée en légende sous le nom σ; résiduel, c'est-à-dire écart-type de la différence des valeurs observés à la régression). •4/15
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Pour chaque saison, la ligne en traits pleins montre les valeurs observées (un point par année), et la droite en tirets est la régression linéaire sur l'ensemble de la période dont l'équation est donnée en légende (je l'ai reproduite ci-dessous pour l'accessibilité). •3/15
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Il s'agit du graphe des températures moyennes à proximité du sol, moyennées sur l'ensemble de la France métro., sur l'ensemble de la journée (jour et nuit) et l'ensemble de la saison considérée (1 point = 3 mois), tirées de la réanalyse «ERA5». (Source précise plus bas.) •2/15
Graphe des températures moyennes de la France métropolitaine, par saison météorologique (hiver = déc. à fév., printemps = mar. à mai, etc.) et par année, du printemps 1950 à l'automne 2024, avec les droites de régression linéaire de ces valeurs. Quelques remarques: 🧵⤵️ •1/15 pic.x.com/8H9y7jdlm1
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@VaeVix Tiens, non, bizarrement ils n'ont pas fait celle-là.
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J'en avais déjà parlé ici, mais depuis il y a 10 nouveaux épisodes qui sont apparus: x.com/gro_tsen/statu…
“Bienvenue en Géozarbie” sur Arte: une série de 2×10 très courts documentaires (environ 10min chacun), consacrés à des bizarreries géographiques (essentiellement des histoires de frontières). Ça a l'air bien renseigné, et c'est rigolo: je recommande. arte.tv/fr/videos/RC-0…
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Summarizing some of the better suggestions in replies to translate “evil” in French: “maléfique”, “malfaisant”, “malveillant”, “vil” and perhaps also “néfaste”.
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@rapha_mil Right now it should work. If it doesn't, make sure you're using “http” and not “https”.
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@zeepity Ah oui, il y a celui-là aussi! Mais si on cherche à dire d'une personne qu'elle est “truly evil”, le mot “néfaste” ne marche vraiment pas bien.
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… “méchant” is too weak, “mauvais” can confusingly mean “wrong”, “vilain” can confusingly mean “ugly”, “malin” can confusingly mean “smart”, “diabolique” is too strong, and “scélérat” (≈“scoundrel”) is too narrow. How did French manage to miss such an obvious word?
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French “méchant” is somewhere between “mean”/“unkind”, “evil” and even “naughty”. French “mauvais” is more like “bad” in all its meanings (including “wrong”). English “evil” as a noun can be translated as “le mal” in French, but the adjective has no good French equivalent: …
It never ceases to annoy me that, while the English adjective “evil” and the French adjective “méchant” have much overlap, they are not identical, and there is no good translation in French of “evil” (as an adjective!) nor in English of “méchant”.
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@monsieurpuyo I suspect there was very little celebration of Christmas around the year 1BC. Reportedly only three people showed up.
Liam Payne, Jimmy Carter, Jean-Marie Le Pen, David Lynch… why do celebrity deaths get so much attention but celebrity BIRTHS don't get any? 😔
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Link: arxiv.org/abs/2411.11568
I missed the fact that there's a new pair of large cardinals axiom in the zoo: “exacting” and “ultraexacting” cardinals. Which I think I understand to be a big deal because their consistency contradicts the “Ultimate L” conjecture (which I understand only very superficially). pic.x.com/vIDoG98Nuq
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@EleuEThana It might be, but then it would be strange not to offer some kind of exposition. The word just drops in like the user is supposed to know (whereas various other terms and facts about the world are explained, like the name of the titular river).
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(And, yes, of course, I'm aware that “porte” means “door” in French. 😅)
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(I'm aware that the Sublime Porte refers to the imperial gate, and metonymically the entire government, of the Topkapı Palace of the Ottoman Empire. But ‘The Sundering Flood’ is European Middle Ages like fantasy, so a reference to the Ottoman Empire would be weird.)
Another word I'm a bit confused about is “Porte”. Morris seems to use it (repeatedly) to refer to the ruler of a city (some kind of mayor), but no online dictionary I can find lists this meaning. Whence did he get this word? x.com/gro_tsen/statu…
I'd LOVE to read your tweets, but my full attention is required to converting my watch from Julian to Gregorian calendar.
RT @doctorow: Our friends and communities are on bad social media networks because they love each other more than they hate Musk or Zuck. L…
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Donc, je raconte dans mon blog que le serveur Web qui héberge mon blog est mort: madore.org/~david/weblog/… (billet pas forcément visible immédiatement, selon votre chance avec le DNS).
ENCORE UNE FOIS? À peine deux mois après la mort de l'incarnation précédente de se serveur betelgeuse [point] gro-tsen [point] net, le remplacement est mort à son tour. C'est hallucinant!␤␤Elles sont en carton, vos Dedibox, @Scaleway_fr? x.com/gro_tsen/statu…
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Link to document with solutions: math.dartmouth.edu/~pw/solutions.…
Seven math puzzles which “you think you must not have heard correctly” by Peter Winkler. I don't like them all equally, but some are quite fun to think about. pic.x.com/PzHhpH3UxT
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@PeterSaveliev Please feel free to suggest additions.
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Link on 🟦天: bsky.app/profile/did:pl…
A few of my favorite Soviet-era jokes: pic.x.com/zRu9FUyEDW
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Much as it pains me to say, I have to agree with the pot: the kettle ✳︎is✳︎ black.
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Just as I was saying yesterday: x.com/gro_tsen/statu…
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Link: indianexpress.com/article/world/…
In other news, prince Muḥammad bin Salmān of Saudi Arabia thinks Iranian supreme leader Ali Khamenei is a ruthless and brutal dictator. #NotTheOnion pic.x.com/4xWykkzXCV
RT @pbeyssac: La pantalonnade française sur le contrôle d'âge continue. Promue par des politiques incompétents techniquement et idéologues,… x.com/reesmarc/statu…
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@vit_tucek I think we're saying similar things. Maybe “domain” wasn't the best word, but I also see “elementary” as a restriction on the tools (theorems and, insofar as this makes sense, definitions/concepts) that may be used in the proof, but not on its length or difficulty.
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@vit_tucek For me, “elementary” means a proof does not use any tools outside a certain domain, which depends on the field (it could be like “no complex analysis”). But the proof can still be tremendously complicated.
Thinking that your enemies and your other enemies are necessarily allied is just as much a mistake as thinking that the enemies or your enemies are your allies but for some reason it rarely gets pointed out as such.
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@Ngnghm … But if you allow arrow constructions as well… I don't know at all. I'm not even sure how one would probably formalize the question. If you find a suitable formalization, maybe try asking on MathOverflow or on Theoretical Computer Science StackExchange.
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@Ngnghm Very good question. If you allow only sum and product types in your recursion, I guess you get the same thing as for CFGs: see, e.g., Berstel & Reutenauer, ‘Noncommutative Rational Series with Applications’ (2010) for more on this. …
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@debasishg @Ngnghm @pigworker I'm on Bluesky as well, FWIW: x.com/gro_tsen/statu… x.com/gro_tsen/statu…
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@LYMFHSR Semble toujours exister dans les TLD: li, gs, vg et la (au moins la page d'accueil s'affiche pour moi — je n'ai pas testé si la recherche et le download fonctionnent derrière).
RT @jeremotographs: Today I was granted access to speak with incarcerated firefighters. ␤␤They told me:␤- they hadn’t showered in 5 days␤-…
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@Anthony_Bonato Here's my attempt to explain why math books do this, and why it is legitimate (although it can certainly be overused, and often is): 🧵🔽 x.com/gro_tsen/statu…
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@xptr_chintololo Here's my attempt to explain why this is not stupid (🧵): x.com/gro_tsen/statu…
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… but it is not true that we should never call things “easy”: doing so has a purpose, it brings valuable meta-information to the reader, and the idea that writing down ✦all the details✦ without hierarchizing them would make proofs easy to read is—just wrong. •15/15
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Now I'm fully aware that some authors overuse “trivial” or “easy” (or the more honest “left as an exercise”) for things that are not at all easy: this is bad mathematical writing, and I won't defend it; … •14/15 x.com/gro_tsen/statu… x.com/gro_tsen/statu…
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… it draws the readers' attention to the statement, entices them to check that it is indeed “trivial” or “easy”, and suggests that they memorize the fact as something that might be important later on. None of this is useless. •13/15
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And similarly, it makes perfect sense to record a statement as a theorem, if only to write its proof as “trivial” or “easy”. This serves to give the statement a name or number, which can then be referred to in a later proof or definition: … •12/15
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So saying “trivial” or “easy” is not giving zero information: the author ✵is✵ telling the reader something about the proof, e.g., “if you're stuck doing something complicated, you're on the wrong path, you probably misunderstood something”. This is valuable! •11/15
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… and if you think these proofs are easy to read because they give all the details, you're wrong. Humans don't read proofs like computers do: it helps them to get some meta-information about what parts are important, what parts are easy, etc. Not just the logical steps! •10/15
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It's tempting to ask “why not give the full details of the proof rather than claim something is ‘trivial’ or ‘easy’?”, but giving the full details essentially means giving a formal proof that can be digested by a proof assistant on a computer, … •9/15
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… in that if you don't find this easy, then you'll stop here and avoid wasting your time trying to decipher much harder proofs later one. Yes, it can be seen as a form of gatekeeping, but it's better to gatekeep in the earlier stages of the text. •8/15
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So claiming that something is “easy” also serves as a kind of check on the reader: the implicit message is “if you don't find this kind of stuff easy, then you probably shouldn't be reading this book in the first place”, which is, in fact, helpful … •7/15
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… you'll take just as long to check them as you would to do the computation for yourself. Now of course “easy” depends on the reader: checking that 543 × 789 = 428 427 is easy for anyone who knows how multiplications work, not for a first grade student. •6/15
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The point here is that the author expects the reader to find it no more enlightening or helpful to follow a proof than to actually do it for oneself. For example, if I claim that 543 × 789 = 428 427, writing the details of the computation won't help you: … •5/15
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“Easy” is less restrictive: it means that the statement follows from a simple argument that the reader should be able to do for oneself. Sometimes one can clarify the type of reasoning, e.g., “follows from a straightforward calculation” is a subcategory of “easy”. •4/15
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… “blueish foobars are weakly blueish” is trivial, as it follows from the definitions and straightforward application of pure logic, and any attempt to explain it further would only waste time and perhaps even confuse the reader. Trivial means “I can't explain further!”. •3/15
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“Trivial” generally means something follows from a straightforward application of pure logic. For example, if a “blueish foobar” in which every element is blueish, and a “weakly blueish foobar” is one in which every cromulent element is blueish, then the statement … •2/15
“Why do math books sometimes write down a statement in a theorem if the proof is going to say that it's ‘trivial’ or ‘easy’?” → This is a valid question, and it actually makes sense (though it can be abused!). Let me try to explain. 🧵⤵️ •1/15 x.com/xptr_chintolol…
RT @Anthony_Bonato: "I will teach myself math from books."␤The book: pic.x.com/g0HRYMBmgw
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@Jastrow75 Je crois que ce que j'ai est la dernière édition papier. C'est une édition «condensée» (mais non abrégée), c'est-à-dire imprimée 9 (ou 16?) pages par page en tout petit, sur un énorme volume au papier hyper fin, et vendu avec une loupe. Pas commode à utiliser.
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… So I assume Sir Godrick is saying that Longshaw is not the most beautiful and ornamental of his manors.
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OK, various online dictionaries suggest that “knop” refers to an ornamental knob, button or tassel, or other kind of ornament; and “ouch” is an ornamental clasp, buckle, or brooch, or setting of a precious stone. …
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@Jastrow75 J'ai une version papier chez moi, au pire je chercherai en rentrant, mais elle est difficile d'accès.
Anyone want to try to guess what “Longshaw, which is as it were the knop and ouch of my manors” means? (Spoken by Sir Godrick in chapter XXXIX.) x.com/gro_tsen/statu…
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@Marco_Piani Cats seem to manage it, though!
You should learn by other people's mistakes. You'll never live long enough to make them all yourself.
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@fare No, but I didn't search because I hadn't heard of them.
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@BallouxFrancois Don't fool yourself in believing she's your cat: it's you who are her human. 😝
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@ngspiensfr @laurentbercot As far as concerns understanding what already exists, I recommend watching this video, which I found very clear in its explanations, and convincing in its arguments about the pros and cons of both ActivityPub and ATproto: x.com/gro_tsen/statu…
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✱ Update: I found this (somewhat old, but still relevant) video by Justin Garrison very interesting in comparing, at a high overview level, how ActivityPub and ATproto work, and what each one's pros and cons are. I very much agree with him. •34/❦ youtube.com/watch?v=wJBCpz…
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@JacqBens Yes, I think you're right!
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@JacqBens (I also have to admit that I can't see much in 3D, so “I think you're on the right track” doesn't convey much geometric intuition beyond “what you say seems eminently plausible to me, but I can't really visualize it”.)
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@JacqBens Not at all, I think you're on the right track as mathoverflow.net/q/365711/17064 suggests in the case of rectangles; and there are certainly a number of cases to consider. But actually proving that all cases have been considered and correctly handled is probably the difficult part.
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@ngspiensfr The interest is certainly there. The time, however, may be harder to find. But I'm certainly willing to discuss such things.
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(La tournure «nonobstant la fixation d'une vitesse maximale autorisée plus faible par l'autorité de police de la circulation en application de l'article R. 413-1» fait que la disposition s'applique même si la vitesse sur le boulevard périphérique parisien est abaissée à 50km/h.)
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Lien vers le décret: legifrance.gouv.fr/jorf/id/JORFTE…
Après huit(?) ans d'«expérimentation», la circulation en interfile (entre les deux voies les plus à gauche) des deux-roues motorisés sur les routes à grande circulation devient définitivement autorisée, sur tout le territoire français, y compris sur le périphérique parisien. pic.x.com/68ZGY5Km2m
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… the Fediverse splits the ❉network❉ into pieces, and tries to be a federation of fiefdoms, whereas Bluesky mostly splits the ❉roles❉, and tries to create a checks and balances system between the roles. Both are good, but serve different purposes. •33/❦ end (so far)
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‣ To say things differently, both Mastodon/Fediverse and Bluesky/ATmosphere attempt to solve the problem stemming from the power concentration of Twitter (and what happens if a madman controls of the center), but they take very different, if complementary, approaches: … •32/
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… whereas on the ATmosphere, you basically have to use the one and only system (Bluesky, which is quite centralized), but the users have some guarantees and power wrt the system whereas on the Fediverse they are enthralled to their server. •31/
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‣ To summarize, on the Fediverse, you have full latitude in choosing your server (or setting up your own, which is IMO the only sane way to use the Fediverse), but then you're stuck with it, or at least your posts are, and you'd better hope it won't go the Twitter path, … •30/
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… This is IMO the single greatest error with Mastodon: they didn't provide for a layer of indirection from the user's account to the server, which would have made it possible to move all of one's posts from one server to another. ATproto has this! •29/
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… And there is simply no way to move a post from one Fediverse server to another: the post is tied to the server, it only really exists on one server (even if others may have copies), and its permalink references that servers. If the server goes, the post goes with it! … •28/
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… For example, on the Fediverse, your identity as a user is inexorably tied to a server. (There is a feature to request that users start following a different account if you wish to change servers, but it's still a different account: you can't move an account.) … •27/
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… but on the other hand, Bluesky gives its users some existence and a much greater measure of control (whereas on the Fediverse, as I mentioned earlier, they have none except insofar as their server gives them some). … •26/
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‣ Generally speaking, while the Fediverse is a very loose federation of servers (like email or the Web), Bluesky is a much more tightly integrated network (though not nearly as much as Twitter, which is just a single site); … •25/
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… so for example, if Bob replies to one of Alice's messages, Alice cannot (even if she has her own PDS) alter the message ex post facto because this would break the hash and therefore the reference. See bsky.app/profile/gro-ts… for more on what this implies. •24/
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The Fediverse has none of these. But the Fediverse also lacks, as I pointed out earlier, any kind of data integrity, whereas this is very much baked in the AT protocol: taking inspiration from Git, it embeds a cryptographic hash in each message reference: … •23/
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So we get features on Bluesky that Twitter can easily implement in its centralized architecture like likes/reposts count, a search function that works well, hashtags and alternate feeds. (Also, the quote-post, but I'm not sure this is architecture-related or just a choice.) •22/
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But it's not just a matter of decorations: Bluesky can offer a search feature that works throughout the network, because, as I pointed out, it distinguishes the “relay” from the PDS, and the relays receive and index everyone's messages. •21/
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‣ On the other hand, Bluesky does offer a number of user features that the Fediverse in no way does. The most obvious of them is that Bluesky looks a lot like Twitter, not just in user interface, but also in functionalities, while Mastodon is worlds apart. •20/
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… perhaps the most apt comparison here is that Bluesky might become like what Google is on the Web: the Web's content is decentralized, but, for most users, Google acts as the entry point and a kind of centralized directory of its content/users. •19/
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‣ So, in many ways, the ATmosphere is far less decentralized than the Fediverse, and in practice it is still a single network with a single operator. Even if it does decentralize eventually, it is predictable that Bluesky will keep a very significant lead and advantage: … •18/
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Furthermore, Bluesky still owns and controls one central piece of the ATmosphere architecture, which is the PLC github.com/did-method-plc… (“Public Ledger of Credentials”, aka “placeholder”) identity provider, which is a kind of centralized directory of every user/agent. •17/
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Each has a different role and could be decentralized. Currently only PDSs are really decentralized and practical for anyone to self-host. Relays require an insane amount of storage to operate, and what views other than Bluesky might be or mean is entirely unclear. •16/
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Whereas the Fediverse (ActivityPub) just has one kind of piece, viꝫ. servers, the ATmosphere has three different beasts: personal data servers (PDSs), relays, and (app) views. In short, PDSs store users' posts, relays aggregate them and views present them to others. •15/
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Discussion of whether Bluesky is decentralized is complicated because nobody really knows what “decentralized” means, and also because Bluesky and ATproto are not the same just like Mastodon and ActivityPub are not the same. •14/
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‣ Bluesky is a rather different beast. It too tries to shift the power balance away from the center, but it does it in a very different way from Mastodon/Fediverse. In short, I would say that Bluesky is less decentralized but empowers users more. •13/
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… So while you can, in principle, run other software, you might encounter interoperability issues. This gives Mastodon devs enormous power on how the Fediverse actually operates. •12/
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‣ Discussion of the Fediverse is complicated by the fact that most of it is powered by the Mastodon software. They are different servers, but they run the same software. And Mastodon has its own additions to the basic ActivityPub protocol of the Fediverse. … •11/
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… Similarly, of course, a server might post bogus replies to a post it hosts: for example, it can change the text in any way it wants. Users might click through to see the original and compare, but few people are likely to do that. •10/
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… So there's no kind of data integrity. At all. If you reply to a post, the author of that post can modify it ex post facto. Maybe your server kept a copy of the original post, and users might see that it differs, but there's little way to tell who changed what. … •9/
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… Each post is generally kept in several copies: on the server of the original author, but typically also on the other server if it's a reply to a post on that one, or if it has replies on that one. But servers can change what they display in any way they want. … •8/
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… Also, the Fediverse works like email, but maybe Web pages are a more apt comparison: basically, a post is a Web page which others can link to: they can send you a notification to say they wrote an answer to you, and then you can set up bidirectional links. … •7/
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… So if, as a user, you want to join the Fediverse, you need to pledge allegiance to a lord (server), who will then own all your posts and ID, like Musk does on Twitter. If you don't like this thought, you need to host your own server. I think everyone should do this. … •6/
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… So while the Fediverse is said to be a “federation”, perhaps a better image is that of a bunch of lordships, each with absolute power over their dominion. They generally talk to each other, but can do whatever they want inside their domain. … •5/
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… from exchanging data to maintaining user identity, to ensuring data integrity (or not). Servers can do anything: impersonate users, modify post content, change timestamps, fake replies, moderate as they wish, refuse to talk to other servers, etc. … •4/
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… your server stores your messages for you, receives replies from other servers and keeps a copy of them. Every server is a fiefdom unto itself: the user has no right, or even any real existence in the protocol, servers are responsible for everything, … •3/
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‣ The Fediverse is easier to understand, because its model is very similar to email. You sign up to a server, which creates an identity for you, and you can use it to exchange messages. Except that messages are (usually) public, it works very much like email: … •2/
Twitter is, of course, a closed and centralized system. Both Mastodon/Fediverse and Bluesky/ATmosphere attempt to replicate (some of) its key features in such a way as to move (some) power away from the center. How do they differ? It's Complicated™. Ongoing thoughts: 🧵⤵️ •1/
Les réponses à ce post, mêlant complotisme, poujadisme, dénonciation de la «pensée unique», sophisme de la «liberté d'expression» ou du «débat», et insultes crasses, sont une excellente illustration des raisons qui conduisent à ce genre de décision. x.com/Polytechnique/…
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@samfbiddle What about targeting tech billionaires? What do the new rules say about that? x.com/gro_tsen/statu…
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My point being: whoever writes the rules on what is deemed to constitute “free speech” is in position to determine what its exact boundaries are, and will reveal, in the hypocrisy of those boundaries, what the writer actually cares about. x.com/gro_tsen/statu…
Do these new rules allow calling tech billionaires in less than favorable terms? Do they allow the expression of curses or the wishing of misfortune upon them or their descendants? How about calling for the realization of such fates? Where does this freedom of expression stop? x.com/samfbiddle/sta…
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@NdeRancourt … these functions have lots of nice properties (e.g., up to a normalization, they give the average value of the projection of C onto a d-dimensional affine subspace), including the fact that they are monotonic under inclusion, which is the fact that you mention for n=3 and d=1.
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@NdeRancourt … typically normalized by dividing by the volume of the (n−d)-dimensional unit ball, so that the d-dimensional intrinsic volume of a cuboid is just the d-th elementary symmetric function of its sides (and the (n−1)-dim intrinsic volume is ½ the surface area); …
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@NdeRancourt More generally, for any convex set C in ℝ^n and any 0≤d≤n we can define a “d-dimensional intrinsic volume” (≈“quermaß”) of C to be the coefficient of degree n−d in r of the volume of the Minkowski sum C + B(r) where B is the ball of radius r …
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@RaoulDeKezel There is some ambiguity as to what the question means, but I take it to mean that we want a set of (polynomial) inequalities on a,b,c,x,y,z.
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@iconjack Regarding U+00A0 NO-BREAK SPACE, unfortunately, many Web browsers and frameworks have the nasty habit of turning it to a normal space. I sometimes use U+202F NARROW NO-BREAK SPACE, though.
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@iconjack Ah yes, U+2212 MINUS SIGN for the win! But did you also notice the U+2062 INVISIBLE TIMES character that I used twice in “a⁢x−b⁢y”? 🧐
RT @EUCourtPress: #ECJ – #GDPR and rail transport: A customer's gender identity is not necessary data for the purchase of a transport ticke…
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@plain_simon OTOH, there are often situations when one can say something about the CRF case from quantifier elimination in the ACF case (and hand inspection of inequalities), but I don't know if this is such a situation.
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@plain_simon Quantifier elimination in the algebraically closed field case isn't too bad (Gröbner bases can do it), but in the real closed case it's horrendous even for very small number of variables, I think, and I don't know of any actual software that will do it.
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@plain_simon Oh yes, quite. In principle, it's a decidable question. But many questions are decidable in principle but computationally infeasible. mathoverflow.net/q/112097/17064 For example, you can in principle compute the n-dimensional kissing number for any specific n by Tarski-Seidenberg.
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(I have no idea if the account tweeting this is in any way official, btw. If only some idiot hadn't disabled any form of verification of accounts on this platform…)
It seems that the mullahs sometimes have a great sense of humor. 😆␤␤[tweet id: 1877011192918487258] pic.x.com/rj1CkV7IZX
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In dimension 2, when 0<a<b and 0<x<y, the rectangle of size a×b fits inside that of size x×y iff a≤x and either b≤y or (b²−a²)² ≤ (a⁢x−b⁢y)² + (a⁢y−b⁢x)². So the question is to generalize this.
There is something at once funny and humbling about this MathOverflow thread in which a bunch of research mathematicians realize they don't know how to answer the question “when does a box of size a×b×c fit inside one of side x×y×z?”. mathoverflow.net/q/282158/17064
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… to seek and learn to recognize who and what, in the midst of hell, is not hell, to make them endure, and to give them space.”␤␤— Italo Calvino, final words of ‘Invisible Cities’ [translation by myself]
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… The first is easy for many: to accept hell and become part of it to the point of no longer seeing it. The second is risky and requires constant attention and training: …
“The hell of the living is not something that will be; if there is one, it is what is already here, the hell we inhabit every day, that we create by being together. There are two ways to avoid suffering it. …
RT @SaarelaHC: Highland Cattle photo of the day pic.x.com/9ydP1z3vV5
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Apparently this painting by George Munger of the White House after it was burned is on display at the White House, perhaps as a form of reminder to the occupant. pic.x.com/J5uu79PSQR
Let me remind any US president who might wish to annex Canada that only once in US history was Washington DC captured and the Capitol burned, and that was in 1814 after the US had declared war in an effort to annex Canada. 😛
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I guess “based on gender” means you can insult women as well. But insulting сіѕ heterosexual males (and only them) is definitely off-limits.␤␤Strangely similar to how self-proclaimed “free speech absolutist” Musk decided that “сіѕ” is off-limits but just about anything else goes.
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Link: transparency.meta.com/policies/commu…
The precise section of Meta (i.e., Facebook)'s new policies on hateful conduct that says you can't call anyone stupid or mentally ill ✽except✽ homosexual and transgender people.␤␤This is what “prioritizing free speech” means, apparently. 🤐␤␤[Link in next tweet.] pic.x.com/S96C3eEURh
Supposedly “isolationist” president-elect of the US is threatening to annex Canada, invade Panamá and declare war on Denmark, while the president-unelect (Musk) is actively working to topple European democracies (UK, Germany, Spain…).␤␤Good thing they're not interventionists! 😑
I know a joke about Georg Cantor, and I can guarantee it's not in your list. x.com/gro_tsen/statu…
I know a joke about Alan Turing, but you won't be able to decide when it stops. x.com/gro_tsen/statu…
RT @3blue1brown: I learned yesterday the video I made in 2017 explaining how Bitcoin works was taken down, and my channel received a copyri…
I know a joke about Kurt Gödel, but you won't be able to decide whether it's funny or not.
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@tshuqwud Yeah, Americans will measure with anything but the metric system. thelanguagenerds.com/2024/27-exampl…␤␤But in all honesty, nobody says “2.75 gigaseconds” for 87 years. 😅
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@mutianning … And I suspect many later uses of “score” (to mean 20, of course) are either similar attempts at sounding old-fashioned, or imitations of biblical language (and the later category might apply to many American evangelicals).
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@mutianning I don't know. I think “score” was already antiquated in English when the King James Bible, which is consciously archaic in its language (e.g., it distinguishes nominative “ye” and accusative “you”) was published. …
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@BillJones2021 Not even all of Switzerland: geneve.ch/themes/culture…
Americans: “the way French people count is unbelievably complicated: ‘quatre-vingt-sept’ for 4×20+7=87? seriously? who would say that?”␤␤Also Americans: “the greatest speech ever made in History, by one of our greatest presidents: ‘Four score and seven years ago…’”
Plans 3D de diverses stations de métro du monde (dont, à Paris: Châtelet, Nation, Montparnasse…). Avec maintenant une version qu'on peut faire tourner: estacions.albertguillaumes.cat
Carte des environs de Paris montrant les endroits où j'ai personnellement pris une photo géolocalisée depuis avril 2016.␤␤Chaque point représente une photo. (C'est quatre fois la même donnée, à différents niveaux de zoom.) pic.x.com/wIE52O7ybz
If we're going to do the “foreigners are over-represented in crimes in European countries”, I think we should keep track of how often South African billionaires try to destabilize democratic governments, because there seems to be a lot of that.␤␤[tweet id: 1875905755892904017] pic.x.com/9hRp35M7O4
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@omartineau … si on n'avait pas persuadé tout le monde d'être nuls en maths parce que les maths «ne servent à rien», on pourrait avoir des systèmes compréhensibles par 100% de la population et qui soient meilleurs.
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@omartineau Il y a des systèmes de vote alternatifs qui sont exactement aussi simples à dépouiller (notamment, sans ordinateur) que les modes actuels. Mais la contrainte d'avoir un système compréhensible par 100% de la population est bien ce dont je me plains: …
RT @SaarelaHC: Highland Cattle photo of the day pic.x.com/1PpYQ3aASY
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@laurentbercot “No homo!”
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… and even throw some items from one bank to the other, I really want to cry “if you can throw something to the other side, you can throw a spool of thread, use it to get a rope across and set up a makeshift bridge that way!”.
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… and too strong for any boat. This is already very hard to swallow and there is nothing remotely similar in real life as far as I can tell, but when we add the fact that the main characters are still able to talk to each other across this supposedly uncrossable river, …
Still reading William Morris's ‘The Sundering Flood’, and I must admit having a hard time suspending my disbelief about the titular river, which is supposed to split a country in two in such a way that nobody can cross it except at its mouth: too wide for bridges, …
I wrote an answer (to an old question) on MathOverflow on how to define a “natural” bijection between the positive natural numbers and the rational numbers using the Stern-Brocot tree: mathoverflow.net/a/485383/17064
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@CocoBel3398211 Je ne pense pas que ce soit vraiment une question de niveau de connaissances mais juste d'habitude à considérer que les maths sont un outil utile pour comprendre et interpréter le monde. Donc de culture de la société (et des journalistes, notamment).
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C'est un peu le paradoxe qu'on nous explique à la fois que les maths ne servent à rien dans la vie courante mais que plein de choses sont jugées «mathématiquement trop compliquées pour le citoyen λ» donc exclues du champ des possibles. 🫤
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Je ne prétends pas que c'est le seul obstacle, mais clairement, à partir du moment où trop de gens se sont convaincus qu'ils étaient nuls en maths, on ferme la porte à toutes sortes de possibilités qui demandent que les électeurs comprennent un peu plus qu'un simple décompte.
J'ai déjà dû le dire, mais une des nombreuses conséquences négatives du manque de culture scientifique de la population générale, c'est qu'on ne peut pas avoir de débat public sérieux sur les modes de scrutins et on reste coincé sur des systèmes bêtes qui ont plein de défauts.
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@ngspiensfr … N ← N+1, S ← S+X₀, and Δ ← (1+1/N)·Δ + (N·X₀−S)²/N (simultaneously), and at the end your average is S/N and variance is Δ/N² (barring probable computation errors of mine, but it should be something like that).
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@ngspiensfr OK, I think this is how I see it without rescaling at each step: instead of keeping running values of ∑1 (number of samples), ∑X (total of samples) and ∑(X²), you keep those of ∑1, ∑X and ∑1 ⋅ ∑(X²) − (∑X)², call them N, S, Δ say; then you digest a new value X₀ by …
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@ngspiensfr Wait, how do you do it in one pass and constant memory without reverting to the mean(X²) − mean(X)² (or rather (∑1 ⋅ ∑(X²) − (∑X)²) / (∑1)²) formula?
RT @ngspiensfr: The thing they always neglect to say about “V = mean(X²) − mean(X)²” is that it is numerically unstable.␤If the number are…
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@SnowFake3 … Now unless you actually have something interesting to say, please stop wasting my time.
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@SnowFake3 … (let alone a representative sample of anything), — or whether the post is supposed to be a caricature of the delusions that some people have about leftists. But I don't care enough to try to understand whether it's cringe stupid or just unfunny satire. …
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@SnowFake3 Sorry, you just broke my Poe's law detector: I can't decide whether you're actually taking the ramblings of a Musk fanboy at face value when he doesn't bother to produce a single shred of evidence about any of the things he claims to have seen on Bluesky, …
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@LesVINCENTs Merci, c'est gentil! 😊
Être intelligent, c'est à la portée du premier connard venu, alors qu'être gentil, ça demande un vrai talent.
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Précédemment au sujet de ces tours nuages: x.com/gro_tsen/statu…
L'histoire et l'architecture des “tours nuages” d'Émile Aillaud, ou cité Pablo Picasso à Nanterre: youtube.com/watch?v=PQnZrJ… — vidéo très intéressante (de façon générale, je recommande cette chaîne YouTube “Le Nouveau Programme” sur l'architecture).
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@Jilcaesel It's usually referred to as “Cunningham's law” (see this funny 🧵🔽), though you might argue that they're not exactly the same thing (one is about complaining that X sucks, another is about posting a wrong answer, which is slightly different). x.com/wacksen/status…
RT @FFmpeg: FFmpeg handwritten assembly language lessons being written.␤␤This week you'll be able to try out te first lesson and submit fee…
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… provoque des sensations de faiblesse, maux de tête, etc., et est très rapidement mortel. Des détecteurs des deux existent, mais ⚠️ un détecteur de CO₂ (qui sert à prévenir des risques d'incendie), ne détectera pas le CO avant qu'il soit trop tard! (Et vice versa.)
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… que le dioxyde de carbone (CO₂) et le monoxyde de carbone (CO) sont des gaz bien différents, le premier est dégagé par toute combustion de produits organiques et provoque une sensation d'asphyxie, le second est dégagé par une combustion incomplète (pas assez d'oxygène), …
Histoire horrible racontée sur Reddit: qqn qui a perdu ses deux parents le soir du réveillon par intoxication au monoxyde de carbone (CO). Le post ne donne pas beaucoup de détails, mais suggère une confusion possible entre CO et CO₂. Donc rappelons … reddit.com/r/france/comme…
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(The point of the ambiguous formulation, of course, would be to have plausible deniability: “no, we didn't order the killing of the former king, it was an o so unfortunate misunderstanding”. But if you can get someone to believe something like that, you probably don't need it.)
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… “do not fear to kill Edward, it is good”. This is told in Christopher Marlowe's play ‘Edward II’ perseus.tufts.edu/hopper/text?do… and Maurice Druon's novel ‘La Louve de France’.␤␤‣ Q: Did this actually happen? Is there historical evidence? Or if it's a legend, whence did it originate?
There's a story that the order to execute the deposed king Edward II was given in the form “Eduardum occidere nolite timere bonum est”, which depending on the placement of a comma before or after “timere”, can mean either “do not kill Edward, it is good to fear” or …
RT @tomgauld: Happy New Year!␤(my cartoon for @newscientist) pic.x.com/zUSKe6ISiL
RT @KyleKulinski: pic.x.com/2xrGe55Ggs

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