person(kelly).
person(judy).
person(ellen).
person(mark).

car(lemon).
car(hot_rod).

likes(kelly, hot_rod).
likes(judy, pizza).
likes(ellen, tennis).
likes(mark, tennis).
likes(mark, lemon).

for_sale(pizza).
for_sale(lemon).
for_sale(hot_rod).

can_buy(X,Y) :-
   person(X),
   car(Y),
   likes(X,Y),
   for_sale(Y), write(X), write(' can buy '), write(Y), nl.