You’ve seen a black hole, but have you ever seen an expander?

I am writing a section on expanders for my book, and to avoid doing that I figured I should try to code up some expanders in tikz. Here’s the famous 3-regular expander based on Selberg’s theorem, connecting x to x+1,x-1,1/x mod p (and 0 to itself) And here’s the same but on 23 and 101 […]