I spent some time reviewing some things in linear algebra (I had forgotten the justifications of some results).

I continued a bit with logic (Goldrei’s book).

I went through some questions I had written up, and Ankified some of the ones I was able to answer.

I started the page Intuitiveness and simplicity tradeoff.

I started reading Goldblatt’s Topoi: The Categorial Analysis of Logic. I suspect I will want to learn category theory at some point, even though I don’t have an immediate use for it.