Anyone who doesn't use that nomenclature on a regular basis is bound to need a refresher legend. The concepts are easily remembered (and used in all kinds of programming). But which direction the e points is less easily remembered.
I learned the details of photosynthesis, the Krebs cycle, and a lot of other basic biochemistry in high school, but I don't remember much of that at all.
I did a fair bit of set work in college, but it took me about a minute to dig some of that up to read and understand the relationship that's being described. I don't think I've worked with sets using actual mathematical notation in over 10 years. It wouldn't have surprised me if I couldn't read it (although I would've found it somewhat distressing).
The weird part is his audience: active students and researchers within the field of CS. They're the ones that I would've expected to be most likely to understand what it said.