(0) Obligation:
Clauses:
zebra(Englishman, Spaniard, Japanese, Ukrainian, Norwegian, Zebra, Water) :- ','(eq(Englishman, Red), ','(eq(Spaniard, Dog), ','(eq(Green, Coffee), ','(eq(Ukrainian, Tea), ','(to_the_right(Green, Ivory), ','(eq(Winston, Snails), ','(eq(Kool, Yellow), ','(eq(Milk, third), ','(eq(Norwegian, first), ','(next_to(Fox, Chesterfield), ','(next_to(Horse, Kool), ','(eq(Lucky, Juice), ','(eq(Japanese, Parliament), ','(next_to(Norwegian, Blue), ','(houses(.(Blue, .(Green, .(Red, .(Yellow, .(Ivory, [])))))), ','(houses(.(Norwegian, .(Englishman, .(Spaniard, .(Japanese, .(Ukrainian, [])))))), ','(houses(.(Dog, .(Zebra, .(Fox, .(Snails, .(Horse, [])))))), ','(houses(.(Parliament, .(Kool, .(Lucky, .(Chesterfield, .(Winston, [])))))), houses(.(Milk, .(Juice, .(Water, .(Tea, .(Coffee, [])))))))))))))))))))))))).
houses(Prop) :- domain(Prop, .(first, .(second, .(third, .(fourth, .(fifth, [])))))).
domain([], X1).
domain(.(X, Rest), Domain) :- ','(select(X, Domain, NewDomain), domain(Rest, NewDomain)).
select(X, .(X, R), R).
select(X, .(Y, R), .(Y, Rest)) :- select(X, R, Rest).
next_to(fifth, fourth).
next_to(fourth, fifth).
next_to(fourth, third).
next_to(third, fourth).
next_to(third, second).
next_to(second, third).
next_to(second, first).
next_to(first, second).
to_the_right(fifth, fourth).
to_the_right(fourth, third).
to_the_right(third, second).
to_the_right(second, first).
eq(X, X).
Queries:
zebra(a,a,a,a,a,a,a).