isa(tom, cat).
isa(spike, dog).
isa(jerry, mouse).
isa(jerrys-nephew, mouse).
isa(timmy, tiger).
would-eat(X, Y) :- isa(X, cat), isa(Y, mouse).
would-eat(X, _) :- isa(X, tiger).
would-chase(X, Y) :- would-eat(X, Y).
would-chase(X, Y) :- isa(X, dog), isa(Y, cat).
hates(X, Y) :- would-eat(Y, X).
likes(X, Y) :- would-eat(Z, X), would-chase(Y, Z).