This has nothing in common with Erlang Programming Language, it's about "method of characterizing geometries based on group theory and projective geometry." https://en.wikipedia.org/wiki/Erlangen_program
Wow, that paper is 45 MB. I read the article and I now looking at the paper, trying to decide whether to spend a day really absorbing it. I assume that you are recommending it. I really like the typography, use of margin text and math notation, etc.
Here is also a talk about this topic, that Petar Veličković gave virtually at the University Erlangen a few weeks ago (and why it is called Erlangen Programme)