A new post in the Homotopy Type Theory series. bartoszmilewski.com/2025/09/22/i...

New blog post in the series on HoTT. bartoszmilewski.com/2025/09/05/m...

Another homotopy blog post. bartoszmilewski.com/2025/07/26/w...

New blog post on homotopy equivalences. Working my way towards HoTT. bartoszmilewski.com/2025/06/20/w...

New blog post about homotopies, fibers and cofibers. bartoszmilewski.com/2025/05/30/f...

In a very Putinesque turn of events, Trump's press secretary Leavitt waved a kompromat file proving that Jeff Bezos partnered with a "Chinese propaganda arm." Soon afterwards Bezos kissed Trump's ass (TM), and the file has been put back in storage. The oligarchs have been tamed.

If I were to teach softwared design, I would use WordPress as the example of the most unusable and buggy UI design.

Another post on categorical topology: the construction of the subobject classifier for presheafs. bartoszmilewski.com/2025/04/21/s...

Working on a new blog post about subobject classifier for presheaves. Decoding just one page out of 600 in Mac Lane Moerdijk.

I'm unable to connect to mathstodon.xyz . PR_CONNECT_RESET_ERROR Is this a known problem? I'm in hotel in Reims, France, and all other connections work just fine.

New post bartoszmilewski.com/2025/03/20/s...

New blog post. bartoszmilewski.com/2025/03/06/u...

I had a nice dinner in Nice. Creative dishes, including a bone-marrow Madelaine for dessert (not bad, considering). But I just don't dig this new fad of oxidized wines (vins jaunes). France has the best wines in the world, and they keep pushing this abomination. I like sauerkraut, but not as wine.

I had no idea one could use math notation and diagrams in Haskell code documentation. hackage.haskell.org/package/mono...

I decided to rearrange the Dao of FP by moving the chapter about Applicatives ahead of Monads. This forced me to separate the discussion of effects into a separate chapter. This goes against the usual approach in category theory, where monads are everything, and applicatives are barely mentioned.

Oh great! Now everybody knows how exciting and dangerous the work of a mathematician is. Our cover is blown. Thank you Apple TV!

New blog post about Game of Life, Advent of Code, and comonad composition. bartoszmilewski.com/2025/01/04/l...

Populations of Siberia and Saudi Arabia are almost equal at 37 mln. Siberia produces 11 mln barrels of oil per day, Saudi Arabia, 12 mln. Yet people in Siberia are dirt poor! Somebody, please, explain it to them.

I don't get the vinyl snobism. I grew up at times when vinyl records and tape were the only media available, and I hated the hissing and the scratching. I dreamed of a more solid and lasting medium, so I welcomed wholeheartedly the arrival of CDs. Wax cylinders, on the other hand, are really cool.

Lately I've been thinking about relativistic ray tracing. Regular ray tracing assumes infinite lightspeed, so it doesn't matter if the light comes from the source to your eye or from your eye to the source. But in relativistic physics, you have to trace the ray backward in both space and time...

I have a solution to the Fermi's paradox. Every sufficiently advanced civilization solves the problem of interstellar transport and communication by harnessing the space-shrinking technology. The unfortunate side effect is that every time they shrink some space in one place, it expands in another...

Lies, damned lies, and AIs

Continuing the series on categorical approach to topology. bartoszmilewski.com/2024/11/16/s...

Season 2 of Silo has just begun (I've read the books).