Re: Art of Prolog Exercise problem

David W. wrote:
busy(Lecturer, Time) :- course(Course, time(Day, Start, Finish), Lecturer, place(Building, Room)),
lecturer(Lecturer, Course), teaches(Lecturer, Day), location(Course, Building), occupied(Room, Day, Time). 

What you probably meant, is:

busy(Lecturer, Day, Time) :-
    course(_, time(Day, Start, Finish), Lecturer, _),
    Start =< Time, Time =< Finish.

Opposed to busy/2, busy/3 depends on the Day _and_ the Time.

Roland
.