jgilchrist

right_of(X, Y) :- X is Y+1.
left_of(X, Y) :- right_of(Y, X).

next_to(X, Y) :- right_of(X, Y).
next_to(X, Y) :- left_of(X, Y).

solution(Street, FishOwner) :-
    Street = [
           house(1, Nationality1,  Color1,     Pet1,   Drinks1,    Smokes1),
           house(2, Nationality2,  Color2,     Pet2,   Drinks2,    Smokes2),