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jeanas.bsky.social
Jean Abou Samra
@jeanas.bsky.social
100 followers 12 following 2.5K posts
PhD student in theoretical computer science at Eötvös Loránd University in Budapest. Mainly here to chat about TCS/math.
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 4h
Thanks a lot!
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 4h
Cough cough. Can anyone please reassure me that it's okay to need time to prepare your lectures/tutorials when you're just a normal human being?
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 4h
Now I have to sit for half an hour and to prepare my lectures now and then (thanks God this concerns only advanced graduate courses yet). And I work as a professional mathematician in academia full time!”

— mathoverflow.net/a/143317/
How do you not forget old math?
I am trying to not forget my old math. I finished my PhD in real algebraic geometry a few years ago and then switched to the industry for financial reasons. Now I get the feeling that I want to do a
mathoverflow.net
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 4h
“After age 40 I also started to lose the ability I always took for granted: to get to the board at any time and start lecturing on some subject in my field with full proofs without any preparation. …
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 12h
Thanks! Here is a more precise question: is it decidable, given two finite sets of generators in ℤ[X]^d or even just ℤ[X], whether the sub-ℤ[X]-modules they generate are isomorphic as ℤ[X]-modules?
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 2d
Doofus algebra question here. Is there any sort of classification of finitely generated modules over ℤ[X]? If this is intractable, what about submodules of ℤ[X]^d? The usual structure theorem applies to a PID, which ℤ[X] is not.
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 2d
Did you see this thread?

bsky.app/profile/jean...
jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 26d
En voilà un autre qui a dû être écrit par un Français…

en.wikipedia.org/w/index.php?...

(lien vers une version fixée de la page car je vais essayer d'arranger ça…)
Filter on a set - Wikipedia
en.wikipedia.org
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 2d
Corrigé, merci. Des mots étaient passés à la trappe quand j'ai reformulé le passage.
jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 3d
What do you think of the page? Does any missing information come to mind (that should go into this article rather than adjacent ones like “Ultrafilter” or “Filters in topology”)?
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 3d
I've just finished a complete overhaul of the Wikipedia page on filters:

en.wikipedia.org/wiki/Filter_...

(compare with the previous version: en.wikipedia.org/w/index.php?...)
Filter on a set - Wikipedia
en.wikipedia.org
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 6d
There is a "Mobile view" / "Desktop" link at the very bottom right of every page.
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 6d
Finally! Wikipedia on mobile will no longer redirect to a "m" subdomain, and instead just serve the mobile version on the main domain. No more confusion when you open a link on desktop that was sent by someone on mobile.

www.mediawiki.org/wiki/Request...
Requests for comment/Mobile domain sunsetting/2025 Announcement - MediaWiki
www.mediawiki.org
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 6d
Attends, le M2 AAG ?!
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 7d
There are really many ways to build a lecture that both gives them ordinals as a useful tool in their mathematical toolkit and entertains them by using them to prove something surprising.
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 7d
Or you could take a game-theoretic angle, use the intuition from some winning strategies to introduce the concept of ordinals, and then use them to do something spectacular, like building a non-determined Gale-Stewart game, or the fact that Hercules always wins against the hydra.
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 7d
But I'm sure the undergrads will be mind-blown if you show them some of the spectacular applications, e.g., existence of A ⊆ ℝ² such that for every d>0 there is a unique pair of points from A which are at distance d.
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 7d
(The Borel hierarchy is much more explicit than “intersection of all σ-algebras containing the open sets”.) Granted, as a set theorist, you probably consider it an unoriginal topic (although I'm not sure the proportion of mathematicians who know about ordinals is all that high).
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 7d
I definitely wish I'd been told about ordinals and transfinite induction much earlier in my mathematical curriculum. A number of things only started to make intuitive sense then, like why Zorn's lemma is true, or what it means to be Borel.
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 7d
“important general references” that are rendered apart from the others. But it is what it is.
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 7d
and only one of {{harvnb}}, {{sfn}} should exist and only one of <ref> and {{r}}, … Ideally, there would be one central pool of named references, everything would be a named reference to that with possibly a page number, and there would be a way to select some of these references as …
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 7d
Now, in the named refs system, you also want to vary page numbers. You can do that with {{r|name|p=…}}. This will add the page number after a colon in the superscript of the footnote.

It's really a mess that these systems coexist, and also {{reflist}} shouldn't coexist with <references>
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 7d
Note that you can still have <ref>{{ cite something }}</ref> in the main text. The <references> doesn't just render its content. It renders footnotes for all the <ref>s, and its content is an invisible pool of <ref>s that you can reuse elsewhere.

{{r|name}} is a shorthand for <ref name="name"/>.
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 7d
To get around this, you replace <references/> with

<references>
<ref name="…">…</ref>
…
</references>

or {{reflist}} with

{{reflist|refs=
<ref name="…">…</ref>
…
}}

and then you write <ref name="…"/> in the main text.
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 7d
The other system is reference names. You can do <ref name="…">…</ref> and elsewhere <ref name="…"/> and the two footnotes will just get the same text.

A problem is that you don't really want to remove some part of the text and discover that it broke a reference far away.
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jeanas.bsky.social
Jean Abou Samra @jeanas.bsky.social · 7d
This makes for two levels of footnotes. In the main text, you have a footnote whose text is in <references/> and reads "Doe 2020". This in turn is clickable and directs to the {{cite something}} in the References section.
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