Sebastian Ullrich

Steps to Reproduce 1. Cause a global AWS outage 2. Run `lake init pkg math`

Easy reproducer

Ist Ladesäule eigentlich der schwäbische Diminutiv von Ladesau

Picture of a house across a lake, framed by autumn-colored trees

Anything can look serene if you crop out all the people around it

With a Settlers cameo even

Another new Map Men already? We are truly blessed

feat(Combinatorics/Additive/VerySmallDoubling): weak non-commutative Kneser's theorem (mathlib4#26660)

For a second I was convinced Mathlib had a file named VerySmallDog.lean

Wispy

For my new job, I am looking for a flat in Munich from January or February, 2026.
Please let me know if you or someone you know is looking for a new tenant. Retoot much appreciated!

Here are the rough parameters I am looking for in a flat:
Rent (warm) […]

[Original post on social.tr0llhoehle.de]

ein goldgelbes Lindenblatt, und drumherum auf den Dielen drei Fabeltiere aus Eicheln, Bucheckern, Lindensamen und Blättern.

#silentsunday

@andrejbauer I didn't think an actual nightmare-inducing toot could exist

A jj history of 5 linear changes

The 5 changes now on separate paths, merging back together in the end

The changes with PRs attached

Okay this is just too fun using `jj`: over the week I've accumulated a good amount of random fixes and improvements on a prototyping branch (pic 1). Using `jj parallelize 'ancestors(@, 5)'`, I can make them independent while keeping the ultimate contents of […]

[Original post on functional.cafe]

Wait why does one out of four British Airways flights have classical music during boarding? What are they plotting?

Despite the odds, I have made it to Glasgow and will be talking about macro crimes and other fun stuff together with @nomeata at the VeTSS summer school tomorrow!

New fear unlocked: getting your laptop splashed on while on the plane by the inexpert opening of a water bottle nearby. I think it'll be okay but jeeze!

Oh, I guess I'm typing this from inside the UK but that notwithstanding, ...

Blocking access to BBC Sounds for listeners outside the UK is a disaster | Letters Letter: As a primary school teacher and an English language educator, Andrés Simón Gil Gil considers the decision a personal and professional loss

Indeed, I now have to listen to stupid ads in between In Our Time episodes again!

https://www.theguardian.com/media/2025/aug/10/blocking-access-to-bbc-sounds-for-listeners-outside-the-uk-is-a-disaster

British Airways, 1.2 stars

"You don't need a .pkpass, just use our app!"

The app:

Without meaning to, I guess this only worked out because I categorized staying for a single event as "visited". I can think of only one country I visited but didn't stay the night: the Vatican

"Europe Level 69" according to countries visited

Nice

https://tenpages.github.io/us-level/eu.html

I am happy to announce that the person in my immediate vicinity who brought a laptop to the swimming pool for work on a Sunday is *not* me

Perfetto UI showing thousands of Mathlib modules closely packed together being built across 32+ threads. After 15 minutes, the degree of parallelism drops to ~10 threads on average when only the "critical path" and some related modules remain, finishing after 6 more minutes.

What building current Mathlib from scratch on a 32-hardware threads machine looks like

A small slice of sun peaks out from below dark clouds and alights a wet street and surrounding buildings in Maxvorstadt, Munich

Brief respite from the rain. What a summer!

Stock photo of pasta alla ruota made in hollowed-out cheese wheel

Me, sophisticated: "Parmesan demon core"

Screenshot of Peak showing a player character leaving behind another character swimming upside down in a hot spring with three capybaras

My friends were kind enough to leave my body with the capybaras

Picture of a very flat raccoon

We were in a wildlife park on Friday and the responsibility fell to me to explain the concept of Flat Fuck Friday

A photo of two booths saying "ELEPHONE" and "LEPHONE"

We are well-equipped at the office. We have booths for both large land mammals as well as French people.

Carleson's Theorem [1] is fully formalised in Lean!

https://github.com/fpvandoorn/carleson/pull/453

1] [https://en.wikipedia.org/wiki/Carleson's_theorem "Carleson's original proof is exceptionally hard to read, and although several authors have simplified the argument there are still no easy […]

"Waning Gibbous" still sounds like a name George Lucas came up with to me

“Bad Apple!!” But It’s 3288 Lean Tactics Spamming VSCode Writing the most useless Lean tactic ever

Well we made it

https://unnamed.website/posts/bad-apple-lean-tactic/

Screen recording on VS Code. In the top half, I do simple changes to a Lean file: adding whitespace, comments, changing proofs. In the bottom file, the library is automatically rebuilt on each file save, always skipping immediately to the end after the touched file has been rebuilt.

And finally a minimum viable demo, fast-forwarding through rebuilding some 1030 files on trivial changes to the `Init.Prelude` root file