I'm a bit embarrassed, about edit activity on this question. Since I don't want to run into an "edit war", I prefer to ask here.
Granted, the question is not asked well, and the OP does not show much work. Nevertheless, he is explicitly asking for a Lisp or Prolog implementation, hence, it seems obvious to me that it can be tagged with lisp and prolog. However, lisp was removed twice by the same editor, without comment. What's the problem?