Wow very nice. Lots of content in here, with no lengthy explanations but useful point-form intuition.

The .epub has very clean math done in HTML (no images), which is a cool way to do things. I've never seen this before. I wonder what the author used to produce the .epub from the .tex?

Update: using Sigil to look inside the .epub, I saw it was produced by `pandoc` and the math is rendered as MathML.