ftree.pl

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

child(X, Y) :-
    parent(Y, X).

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

grandchild(X, Y) :-
    child(X, Z), child(Z, Y).

male(tom).
female(pam).
male(bob).
female(liz).
female(ann).
male(pat).
male(jim).

different(X, Y) :-
    X \= Y.

father(X, Y) :-
    parent(X, Y), male(X).

mother(X, Y):-
    parent(X, Y), female(X).

brother(X, Y) :-
    parent(Z, X), parent(Z, Y), male(X), different(X, Y).

sister(X, Y) :-
    parent(Z, X), parent(Z, Y), female(X), different(X, Y).

predecessor(X, Y) :- parent(X, Y); parent(X, Z), predecessor(Z, Y).

sibling(X, Y) :-
    brother(X, Y); sister(X, Y).

aunt(X, Y) :-
    parent(Z, Y), sister(X, Z).