Comments on Liens vers quelques fils Twitter

jonas (2020-09-08T12:36:38Z)

Re <URL: > on non-breaking spaces. I believe that CharlotteBuff's reply <URL: > is correct. The relevant reference documentation is <URL: >, it's quite complicated and I don't understand most of it.

jonas (2020-08-28T01:59:31Z)

Re <URL: > “What killed MathML”, my opinion differs. What killed MathML is that it was designed without a backwards compatible upgrade path. There's no reasonable way to put both MathML and fallback HTML into the same webpage such that MathML-capable browser would display the MathML, whereas other browsers display the HMTL. As a consequence, no webpage author wants to start using MathML, because then the majority viewing their page with an old browser will get a worse experience than if they don't use MathML, and no browser maintainer wants to add MathML, because too few webpages are using it.

jonas (2020-02-19T15:42:58Z)

Re <URL: > pixel coordinates. I generally prefer convention (C), which puts the boundaries between pixels to nice grid points. I have met both software libraries that use (C) (eg. cairo) and ones that use (A). I've seen (B) used in only one case. You want to describe a 3D scene in software, and you want to define the color (or any other property that is a function of the location) of a surface using a raster image. In that case, it is important to be able to control the color at the very edges of the surface.

Re <URL: >: finally a question I'm competent in. Please ask more such questions. I admit this one did turn out quite difficult. Try the following command.

convert input.png -background transparent -fill "#880000" -font "Helvetica-Bold" -pointsize 24 \( label:ORIGIN +distort affine "%[fx:w/2],%[fx:h/2] 0,0" \) \( label:MARK +distort affine "%[fx:w/2],%[fx:h/2] 400,100" \) -layers flatten output.png

This writes "ORIGIN" centered on the point (0,0), and "MARK" centered on the point (400,100). The output will be cropped the same as the input image, so you will see only a quarter of the "ORIGIN" label in the output – I used this as an example to show you that the text is centered. The captions are centered based on their bounding box, which would give you ugly results if you wrote several captions in lowercase letters and tried to align them. Normally you could use the -repage operator to shift the captions to a given position, but that would make it difficult to center the texts, which is why I use +distort. I tested the above with ImageMagick 6; it may work with ImageMagick 7 but I can't guarantee.

jonas (2020-01-06T12:28:46Z)

Re your Star Wars question <URL: >. For how we learned the name "Palpatine" out of universe, see <URL: > that question on Sci Fi Stack Exchange.

jonas (2019-11-21T23:11:40Z)

Re <URL: >. The lang attributes in HTML are useful for few things other than quotation marks.

(1) They decide whether italic cyrillic letters should appear as of they are Serbian or Russian letters, since they're encoded as the same one cyrillic script in Unicode. Testcase: <i lang="ru">т</i> <i lang="sr">т</i>. Similarly, certain kanji characters should look different in Japanese, simplified Chinese, and traditional Chinese, and the lang attribute can decide how to render them.

(2) They decide to uppercase "i" the Turkish way. Testcase: <span style="text-transform: uppercase" lang="en">i</span> <span style="text-transform: uppercase" lang="tr">i</span>. There are a few more related language dependencies mentioned at <URL: >.

jonas (2019-09-19T19:28:19Z)

In <URL: >, you ask about the altitudes of a spherical or hyperbolic triangle. You say in later tweets that the three altitudes intersect (possibly in the projective plane only). Let me add an alternate proof though.

Consider a triangle ABC on the hyperbolic plane. The Reiman book [1] gives the following proof that its three altitudes intersect in the projective extension. Take such a Caley-Klein model of this plane where the fundamental conic is a circle and the center of the circle maps to A. If a line is incident to A, then the same lines are orthogonal to it in the model as in the hyperbolic plane. Thus the three altitudes of the triangle ABC in the model map to altitudes in the hyperbolic triangle. You already know that the altitudes of a Euclidean triangle intersect, thus the altitudes of a hyperbolic triangle intersect too.

[1]: Reiman István, ''A geometria és határterületei''. (1986) Gondolat, Budapest. The extended edition ''Geometria és határterületei'', (1999), Szalay, Kisújszállás is more available.

jonas (2019-09-13T18:21:10Z)

Re <URL: >, Szathmári Sándor's novel <i>Kazohinia</i> is somewhat similar to that idea. The novel is available in Hungarian, Esperanto, and English; and either the Esperanto version is a translation from Hungarian by the author, or both the Hungarian and Esperanto versions are original.

Let me summarize the relevant parts of the story. The protagonist Gulliver arrives to an undiscovered island called Kazohinia. The society of humans on the island is strange in a way that I will not describe here. The island has an autonomous enclave (reservation), populated by humans who are deemed as permanently unfit to the majority society. Gulliver visits this enclave in the middle section of the book. The enclave has its own society very different from that of the rest of the island. Its habits match some of what you are asking for. People, including children, eat in enclosed spaces where nobody else can see them. They talk about food in euphemisms, and they do not like to admit that eating is an essential requirement of life. If it is found out that a person has fed another and they aren't spouses, then they will be identified as low status as if they were a prostitute and a client for a prostitute. People often urinate in public view. The book does not mention sex anywhere, because the protagonist is married in his homeland so it doesn't come up, so we never learn the people's attitudes about it.

jonas (2019-09-06T11:24:52Z)

Re <URL: > migrating phone numbers from one mobile phone to the other. Yes, I also noticed that every phone uses subtly different formats for the address book. I tell about my experiences with converting them at <URL: >.

jonas (2019-08-29T21:20:09Z)

<URL: > recommends the book Jürgen Richter-Gebert, "Perspectives on Projective Geometry", Springer (2011). I've since bought a copy of this book, and I'm very satisfied it. I learned a lot from it. It is on the bookshelf close to my desk, next to the other three geometry reference books that I own.

alcidenikopol (2019-08-22T18:18:31Z)

Concernant la théorie homotopique des types, Vladimir Voevodsky soutient dans cette conférence que l'entreprise du groupe Bourbaki, très remarquable et intéressante à ses débuts - du fait du sérieux et du talent de ses membres - s'est toutefois quelque peu enlisée à moment donné. Et il lui semble que cela s'explique en grande partie par l'insuffisance de la théorie des ensembles (ZFC, plus particulièrement) sur laquelle elle s'appuie.

C'est pour dépasser ce problème qu'il s'est intéressé à d'autres fondations possibles des maths, en premier lieu à la théorie des catégories (il estime avoir fait un grand progrès en comprenant que les catégories ne sont pas, à l'en croire, des "ensembles en dimension supérieure", comme c'est généralement soutenu, mais plus exactement des "ensembles partiellement ordonnés en dimension supérieure", les simples "ensembles en dimension supérieure" étant plutôt les groupoïdes, dans le même ordre d'idées). Quoi qu'il en soit, la théorie homotopique des types (avec axiome d'univalence) se présente comme un système fondationnel complet - à l'instar de ZFC, de ce point de vue - contrairement à la théorie des catégories (trop peu ambitieuse, faut-il comprendre).

Bon, n'étant moi même qu'un profane, je serais bien incapable de savoir si cet élément (glané parmi diverses vidéos de vulgarisation) peut faire évoluer le débat entre personnes éclairées, mais, à toutes fins utiles, "je pose ça là", comme on dit maintenant. :-)

JML (2019-08-21T08:49:18Z)

Concernant le médicament au durian, il faut voir qu'il y a des variations individuelles d'origine génétique (plus tout ce qui se rajoute par-dessus) dans la perception des odeurs (et du “goût” donc).
Quand j'étais petit on me faisait avaler un médicament (antibiotique ?) au goût d'orange vomie. Il paraît clair que je devais être un des rares enfants à percevoir l'arôme d'orange utilisé comme ayant un très net arrière-goût de vomi…

Qu'est-ce que ça t'apporte de twitter sur twitter plutôt que sur ton blog ? (à part que tu ne supportes pas un message de blog de 3 lignes.) As-tu plus d'audience, de réponses ?

Vicnent (2019-08-19T15:32:50Z)

@Ruxor : oui, là dessus, je te rejoins complétement, il manque clairement un outil de tri qui pourrait également représenter les branches de commentaires du fil initial voire même des commentaires eux mêmes…

Ruxor (2019-08-19T12:29:13Z)

@Vicnent: Le problème c'est surtout que des bouts intéressants du fil peuvent être cachés dans les réponses d'autres personnes (et les réponses à ces réponses), c'est surtout ça que je reproche à Twitter de ne pas montrer de façon intelligente, et si le threader est utile pour compiler en une seule page toute une série de tweets d'une seule personne, il n'a pas de fonction pour rassembler aussi les réponses d'autres personnes (ce qui demande forcément une sélection manuelle, ou, au moins, manuellement assistée).

Vicnent (2019-08-19T12:12:14Z)

tu peux aussi ajouter à la fin du thread un tweet avec le texte exact de la ligne suivante :
@threader_app compile
ce qui va déclencher un process de compilation

Exemple sur ce thread de à propos de NP <URL: />
qui va donc donner <URL: />
le thread est numéroté via le n° du tweet par ailleurs ;
J'imagine que tu n'es pas fan de laisser les objets ainsi déportés sans maitrise mais tu devrais pouvoir bidouiller rapidement un petit CRON qui va regarder parmi tes derniers tweets, ceux qui sont liés entre eux par au moins une série de 4 par exemple. Et ensuite, tu peux faire un petit encart automatique qui renvoie vers l'index de ces thread, chez toi ou sur tweeter si les gens veulent commenter / ajouter / etc…

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