I didn't grok anything at first actually. I had familiarity with Prolog and wanted a refresher, so I decided to take a look at implementation attempts done in other languages. I found one which did it in a few lines of Javascript, and you can find the full read and implementation here: https://curiosity-driven.org/prolog-interpreter . My apologies if I didn't make it clear that this is a port of the original write up - I did include this in the first paragraph of the README though, so maybe I should have been clearer?

Originally, I was trying to learn Kotlin along with wanting a refresher in Prolog, so I attempted to do the port using Kotlin and gave up half way though. I didn't have the patience to try to grok too many things at once, so I decided to go with Python due to it's simplicity, popularity, as well as the fact that I'm a lot more fluent in it than I am in Kotlin.

Anyways - sorry if I'm going off track. To answer your question, I grokked the implementation details through porting / refactoring the original code. The concepts / unification I was already familiar with from taking a university course which involved Prolog and from using it in a large AI project. From what I remember, it took me quite a long time to grasp the language and its power!!