I've enjoyed reading your two recent essays here https://www.deobald.ca/essays/ @deobald :)

Another one of my useless observations 🙃 Let A be a commutative (semi)ring. An element a in A is called nilpotent if there exists n ∈ ℕ = {0, 1, 2, …}such that a^(n + 1) = 0. It is a well-known fact that the set of nilpotent elements forms an ideal: We have 0^(0 + 1) = 0 a^(m + 1) = 0, b^(n + […]

New blog post just dropped 😎 https://jdw.codeberg.page/blog/locally-free-modules/

Are there more people from algebraic geometry, commutative algebra, etc. on mastodon? Somehow I'm mostly following type theory people (which I'm also interested in, even though I'm even more of an amateur in type theory than in AG 😅) #AlgebraicGeometry #commutativealgebra

If A is an endomorphism of an n-dimensional vector space, consider the polynomial B(X, Y) := det(X*id + Y*A) in the variables X, Y. Does this have a name or an established notation? I found this proposition in Bourbaki's Algebra which computes that B(X, Y) = […] [Original post on mathstodon.xyz]

I couldn't sleep all night, because this question crossed my mind (so as with all nightly mathematical thoughts, there is some danger of embarrassment): What is the simplest (or any) example of an affine algebraic variety X and a rank 2 vector bundle E on X which doesn't split as the direct sum […]

RE: https://mathstodon.xyz/@jdw/115909250586561061 Now I installed Minecraft instead

Around once a year I try to install Lean for one hour, it doesn't work and then I give up. Already looking forward to next year 🥲

Warning: Useless thoughts. In a mathoverflow comment https://mathoverflow.net/questions/507049/precise-meaning-of-picking-a-basis#comment1320734_507049 @ncf asks if it is possible to define the product of an unordered pair of elements (of a commutative monoid, say) without "choosing" a first […]

Lombardi-Quitté's *Commutative Algebra: Constructive Methods* is a great book, but I wish they had opted for a slightly less concrete and more abstract POV… I guess there are two kinds of people interested in constructive mathematics – the hardcore abstract people from type theory and (higher) […]

RE: https://mathstodon.xyz/@jdw/115850301133225584 So far, it's really fun and I'm learning a lot!

Das liest sich überraschend gut: https://ard.social/@tagesschau/115882843370299712

ok my dudes it's 2026 and i'm calling it. a supergroup led by @pojntfx and @jorge ends up steering the #cloudnative crowd back to the fun of desktop software development. a small army of distributed systems nerds will make #localfirst on the desktop happen, since every large backend system is […]

I'm starting a new job tomorrow and am a bit nervous.

We are looking for an experienced Android UI developer for https://github.com/deltachat/deltachat-android. Native Java, close to the system, with minimal deps and fluff. Networking/encryption/persistence is not part of the job as it happens in https://github.com/chatmail/core Remote collab is […]

With the momentum of #diday here on mastodon I'm almost a bit sad that I'm already pretty independent and there's not that much left for me to do… I don't use Windows, Apple, Android, Google, YouTube, GitHub, WhatsApp, … The only thing left is spotify – I should probably get around to finding […]

RE: https://mathstodon.xyz/@jdw/115805184268670193 According to an article by @FediTips in order to quote a post in a reply, I have to paste the link to the post I want to quote at the end of my reply. But in the post quoted from this post, that didn't work. Am I doing something wrong? […]

A friend of mine about his dad: »He doesn't use google anymore, instead he talks to ChatGPT. But he doesn't even think about what he wants to search or ask, he just starts talking wildly and whatever comes as a reply is 100% true for him.«

I just signed the petition https://epetitionen.bundestag.de/petitionen/_2025/_07/_14/Petition_183950.nc.html to the German Bundestag against the creation of givernment records of trans and non-binary citizens. After that I realized that the Bundestag site for […] [Original post on mathstodon.xyz]

Global history may be my favourite subfield of history (as a passive consumer). Recently I started reading Förster's recent book on German Military History which despite its name takes a pleasantly international viewpoint. Other good books I've read are Osterhammel's Transformation of the World […]

Is there a general theory of ideals in polynomial rings of the form I = <f_1, ..., f_r> where f_i = m_i - m'_i and m_i, m'_i are monic monomials (products of the polynomial variables)? Viewing the polynomial ring as the monoid ring over the free commutative monoid <T_1, ..., T_n>, the quotient […]

I encourage you to be even nerdier

I’ve remembered the history of the 30 years war quite well.

I just made a bet with my friends that if I open reddit or youtube in the next year, I'll have to donate 3k€ to some charity. I hope that with this financial incentive, I can keep my streak for the whole year (in the past I usually failed after a few weeks or months) and I'm already looking […]

PSA: Space Cadet Pinball is available on FlatHub: https://flathub.org/de/apps/com.github.k4zmu2a.spacecadetpinball #linux #gaming

I'm thinking about starting a mastodon account for a (German) political organization which is so far only available on the big American platforms. However I'm not sure what might be a good instance to host the account. Any suggestions? #fediask

RE: https://mastodon.design/@modal/115667365166451345 I want this to happen

I really hope @Signal will provide official flatpaks (via their own repository if they want to be in complete control)

#pastpuzzle 404 🟩🟩🟩🟩 (0) ▪️▪️▪️▪️ ▪️▪️▪️▪️ ▪️▪️▪️▪️ 1/4 🥇 https://www.pastpuzzle.de Endlich mal wieder

RE: https://mastodon.social/@cmconseils/115616453811325078 Zum Thema »Stadtbild«…

Working with constructively with direct sums indexed by sets without decidable equality can be confusing. (Note that the direct sum is not contained in the direct product, there isn't even a map!)

I just found a question in my notes which I asked myself years ago. Maybe someone enjoys proving the claim or thinking of a counterexample: Let X and Y be topological spaces. The product topology on X × Y certainly satisfies the following two properties: 1. The first projection X × Y → X is […]

TIL that the official #Wikipedia app (available on #fdroid) contains a nice #history #game where each day you get to play five rounds in each of which you have to guess which of two historical events that happened on the same date as the current day happened […] [Original post on mathstodon.xyz]

I wrote a small blog post on the equivalence between ℤ-graded rings and affine schemes with a 𝔾ₘ-action: https://jdw.codeberg.page/blog/graded-rings/

I sometimes see posts with »subpost« as content warning. What does that mean? @ah

@typst is fun!

15 years after the first circulation in the form of lecture notes for Ravi Vakil's algebraic geometry class, his popular introduction to Grothendieck-style algebraic geometry »The Rising Sea« is now available for preorder as a published book by Princeton […] [Original post on mathstodon.xyz]

Can we do the thing we did about #chatcontrol about #wealthtax#chatcontrolnext?

This might be a stupid question, but is there some way to open mastodon links with my Android mastodon client by default? I guess it's difficult because of the different domain names used by the various mastodon servers… Is there something like `mailto:`?

A discussion by the mathematician and historian of mathematics W. Scharlau of the unpublished novel »Eine Frau« (»A woman«) by Hanka Grothendieck, the mother of Alexander Grothendieck. I wish so hard that there was some way to get a copy to read, it sounds super interesting! Appearantly there […]

A discussion by the mathematician and historian of mathematics W. Scharlau of the unpublished novel »Eine Frau« (»A woman«) by Hanka Grothendieck, the mother of Alexander Grothendieck. I wish so hard that there was some way to get a copy to read, it sounds super interesting! Appearantly there […]

Can someone explain to a non-logician what locales have to do with »structures« in proof assistants? I come from an algebraic geometry background and I know about locales mostly as a special class of topoi, or as a constructive alternative to topological spaces. I know very little deep […]

When doing pure rust and the compiler is happy (and you're doing proper error handling) you can be reasonably sure that your program won't crash. So when I'm using the Rust bindings to GTK for GUI programming and my program crashes, I'm extra disappointed :(

I finally sat down and imported the books I read over the last years to my bookworm profile @jdw. Check out Bookwyrm (https://joinbookwyrm.com/) if you like #books and the #fediverse#booksand check out my profile if you're interested in the books I read 🙂

There now is a recording of the ad-hoc #datenspuren "usable end-to-end" talk from friday evening, german audio only https://app.media.ccc.de/v/ds25-603-usable-end-to-end-security-with-delta-chat-and-chatmail