I'm happy to announce that I have joined &Truth, which exited stealth today with a feature in the NY Times, as Chief Lean Officer alongside my continued role at the Lean FRO. Coming back to program verification after many years of working on making Lean an ideal foundation for it feels awesome […]

Not sure why they put the functional programmers in the UN Security Council room but I'll take it Featuring @fancytypes talking about representing binders in Dependent Haskell

Arrived in Malaga for Lambda World. Actually my first non-academic conference, I think? ...oh my God I love flying over the Alps

My mind cannot conceive of a better break. Please tell me about yours!

Vale Margaret Hamilton. She was a Software Engineer. She was the _first_ Software Engineer because she defined the term, Software Engineering: "When I first came up with the term, no one had heard of it before, at least in our world. It was an ongoing joke for a […] [Original post on aus.social]

wavy

Some 6 months after I adopted Mathlib to the module system, Mathlib will soon start warning any dependent libraries that have not yet adopted it. This will allow them to make more ambitious refactorings (e.g. https://github.com/leanprover-community/mathlib4/pull/38198) enabled by the module […]

Summer is over, time for even more tea

Today I learned that you can just rent AMD EPYC Genoa 9554P with 64 cores and 768GB RAM at $1.78/hr. That's crazy. ...well, you no longer can, at this particular provider, because I took the last one

Let's do some performance exploration of the Anthropic FLT proof (https://github.com/anthropics/fermats-last-theorem) To set the scene, we are talking about 60,475 Lean modules in FLT on top of 8,312 already part of Mathlib. However, these two file sets are not of quite the same shape: the […]

> A rat king lived in the tower walls, but it knew better than to send its rat knights against a Craftswoman. They knelt as she passed. I'm back to the Craft series after one more Wandering Inn book and the small-scale world building mentioned in passing (heh) is once more on point.

The real numbers are the friends we made along the way

Claude has seen better days

Unethical pro-tip: use Windows paths in your commit message to make your commit go faster

Well this was a rather delightful weekend optimization surprise https://github.com/leanprover/lean4/pull/14962

perf: split `Core.Context` into hot and cold subobjects by Kha · Pull Request #14962 · leanprover/lean4

-0.5% instrs, -1.3/1.8% wall-clock core/Mathlib withReader can never reuse the Context record as the caller is owning a reference, so every withRef, withOptions or withIncRecDepth pays one referenc...

github.com

Best-written article I've seen this week https://www.theguardian.com/lifeandstyle/2026/aug/19/acai-chipotle-and-gnocchi-and-other-words-you-are-probably-mispronouncing

Açaí, chipotle and gnocchi – and other words you are probably mispronouncing

The English language can seem designed to trip us up, whether we’re greeting a colonel or travelling to Worcestershire. Here are some of the biggest stumbling blocks

theguardian.com

After who-knows-how-long, I have completed all top 100 25x25 puzzles in Nonograms Katana What... what do I do now

Seems like you only need to switch continents to get asked again if you're a student

My latest cartoon for @newscientist.com

"I see you're wearing Scarpas, are you a climber?" - "No, I'm German."

What, how does this Portuguese hotel have loose-leaf pu-erh. This is amazing.

My latest cartoon for @newscientist.com. Inspired by recent news about the SpudCell. NS subscribers can read about it here: www.newscientist.com/article/2532...

At the Lean workshop, Ningning Xie presented Lott, a WIP Ott-like embedded into Lean. Formal typing rules were one inspiration for the implicit quantification feature of Lean 4 so it's beautiful to see this coming full circle, properly annotated by the Lean language server.

Lean workshop keynote accomplished, find me there/at ITP to ask me lots more questions!

GitHub Inactions

Just realized I can use jj's expressive revset language to eject a parent from a merge commit without having to look up the names of all the other parents ``` jj rebase -s wstt -d 'wstt- & ~xklum' ```

Düsseldorf will be integrated into Bavaria with the next update to rectify this issue https://github.com/microsoft/dusseldorf/issues/80

Düsseldorf isn't in Bavaria · Issue #80 · microsoft/dusseldorf

Your readme says: This project is often stylized as duSSeldoRF, following a common practice to use place names. The beautiful Bavarian city Düsseldorf is one of the few places in the world with the...

github.com

It happens. God I love Rhythm Heaven Groove

Hiking friends #cordelpics