% Family relationships knowledge base
% Facts about parent relationships
parent(tom, bob).
parent(tom, liz).
parent(bob, ann).
parent(bob, pat).
parent(pat, jim).

% Facts about gender
male(tom).
male(bob).
male(jim).
male(pat).
female(liz).
female(ann).

% Rules to infer other relationships
father(X, Y) :- parent(X, Y), male(X).
mother(X, Y) :- parent(X, Y), female(X).

grandparent(X, Z) :- parent(X, Y), parent(Y, Z).
grandfather(X, Z) :- grandparent(X, Z), male(X).
grandmother(X, Z) :- grandparent(X, Z), female(X).

sibling(X, Y) :- parent(Z, X), parent(Z, Y), X \= Y.
brother(X, Y) :- sibling(X, Y), male(X).
sister(X, Y) :- sibling(X, Y), female(X).

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

% Query examples:
% ?- father(tom, bob).
% ?- grandfather(tom, ann).
% ?- ancestor(tom, jim).
% ?- sibling(ann, pat).