language(smalltalk). language(lisp). language(prolog). essence(smalltalk, objects, 'message passing'). essence(lisp, lists, 'recursive functions'). essence(prolog, relations, 'logical inferencing'). history(smalltalk, inventor('Alan Kay'), date(1980)). history(lisp, inventor('John McCarthy'), date(1959)). history(prolog, inventor('Alan Colmeraur'), date(1971)).