The main point of this discussion is that Prolog, and logic in general, is much more powerful than the basic sort of expert system using IF..THEN rules and backward chaining. If you want to get involved in reasoning with facts then you really do have to go to the extra trouble of learning Prolog and developing a program. It is worth saying that while Prolog isn't an impossibly difficult language, people vary in their ability to absorb it and use it naturally. That is you might spend a lot of time learning Prolog never to get very far. If you are planning an expert system project it is worth considering a simple expert system shell because most of the really cost effective applications are simple enough not to need first-order predicate calculus.