% Simple Forum program demonstrating basic predicates
% Defines family relationships

parent(tom, bob).
parent(tom, liz).
parent(bob, ann).
parent(bob, pat).
parent(pat, jim).

grandparent(X, Z) :- parent(X, Y), parent(Y, Z).

ancestor(X, Y) :- parent(X, Y).
ancestor(X, Y) :- parent(X, Z), ancestor(Z, Y).