% Family relationships
parent(tom, bob).
parent(tom, liz).
parent(bob, ann).
parent(bob, pat).
parent(pat, jim).

% Define ancestor relationship
ancestor(X, Y) :- parent(X, Y).
ancestor(X, Y) :- parent(X, Z), ancestor(Z, Y).

% Query examples:
% ?- ancestor(tom, jim).
% ?- ancestor(tom, X).