I know, but Erlang is pretty different from Prolog in how you actually write it. Erlang is a functional, sometimes-imperative language with heavy concurrency emphasis. Prolog is a lot more "define rules and let the runtime figure out relations". The syntax is superficially similar, and I'm aware that Erlang's original interpreter was Prolog, but they're fundamentally pretty different in how you actually write it.

At least that's my understanding.