SWISH -- SWI-Prolog for SHaring

/* Given information:
 * dance: Friday 1-4
 * art: Monday 10-11, Wednesday 10-11, Friday 10-11; 
 * 		Monday 11-12, Wednesday 11-12, Friday 11-12
 * music: Monday 11-12, Wednesday 3-4, Friday 3-4;
 * 		  Monday 2-3, Wednesday 2-3, Friday 11-12
 * film: Monday 11-12, Wednesday 11-12, Friday 12-1;
 * 		 Monday 12-1, Wednesday 12-1, Wednesday 3-4
 * lunch: 12-1 or 1-2
 */
solution(P1,P2,P3,P4,P5,P6,P7,P8,P9,P10,P11,P12) :-
    period(P1), period(P2), period(P3), period(P4), period(P5), period(P6),
    period(P7), period(P8), period(P9), period(P10), period(P11), period(P12),
	\+ P3=P4, \+ P6=P7, \+ P9=P10.
period(P) :- day(D), time(T), P is 100*D+T, \+ taken(P).
% days
day(1). day(2). day(3). day(4). day(5). 
% 1-hour timeslots available
time(10). time(11). time(12).
time(13). time(14). time(15).
% Monday
taken(113). taken(115).
% Tuesday: nothing available
taken(X) :- X // 100 =:= 2.
% Wednesday
taken(313). 
% Thursday: nothing available
taken(X) :- X // 100 =:= 4.
% Friday
taken(513). taken(514).