Re: Art of Prolog Exercise problem

From: Roland Illig <roland.illig@xxxxxx>
Date: Mon, 10 Oct 2005 11:48:15 +0200

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).


Slightly reindented:

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).

The lecturer() line is superfluous. If there is a course(C, _, L, _), it is obvious that lecturer(C, L) is also true.

Same for teaches(L, D).

Same for location(C, B).

This leaves us with the following:

busy(Lecturer, Time) :-
    course(_, time(Day, _, _), Lecturer, place(_, Room)),
    occupied(Room, Day, Time).

This means: Lecturer is busy when there is any course in the same Room and on the same Day, no matter what the lecturer of that course is.

Roland
.

References:
- Art of Prolog Exercise problem
  - From: David W .

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