I did have to learn some Prolog when I was studying CS and back then it was one of those "why do we have to learn this when everybody is programming in C or Turbo Pascal" (yes, I'm old). For some strange reason things clicked for me quicker with Prolog than Lisp, which I now find quite ironic given that I've been using Emacs for since the early 1990s.
Anyway, a recent post over on Hacker News alerted me to a book called "The Art of Prolog". From what I can tell it's out of print but this is not a book that is very hard to find.
So that'll be the reading material sorted for the next week or three.