nextto(X, Y, List) :- iright(X, Y, List).
nextto(X, Y, List) :- iright(Y, X, List).
iright(Left, Right, [Left, Right | _]).
iright(Left, Right, [_ | Rest]) :- iright(Left, Right, Rest).
zebra(H, W, Z) :-
    H = [house(norwegian, _, _, _, _), _, house(_, _, _, milk, _), _, _],
     member(house(englishman, _, _, _, red), H),
     member(house(spaniard, dog, _, _, _), H),
     member(house(_, _, _, coffee, green), H),
     member(house(ukrainian, _,  _, tea, _), H),
     iright(house(_, _, _, _, ivory), house(_, _, _, _, green), H),
     member(house(_, snails, winston, _, _), H),
     member(house(_, _, kools, _, yellow), H),
     nextto(house(_, _, chesterfield, _, _), house(_, fox, _, _, _), H),
     nextto(house(_, _, kools, _, _), house(_, horse, _, _, _), H),
     member(house(_, _, luckystrike, oj, _), H),
     member(house(japanese, _, parliaments, _, _), H),
     nextto(house(norwegian, _, _, _, _), house(_, _, _, _, blue), H),
     member(house(W, _, _, water, _), H),
     member(house(Z, zebra, _, _, _), H).

zebra1(Houses, WaterDrinker, ZebraOwner) :-
        zebra(Houses, WaterDrinker, ZebraOwner), !.
solve :-
    repeat(I),
    zebra1(Houses, WaterDrinker, ZebraOwner),
    I=:=1000.

benchmark :-
    S is cputime,
    solve,
    T is cputime-S,
    write(T).