father(john, peter).	/* John is the father of Peter. */
father(john, mary).
father(david, liza).
father(david, john).
father(jack, susan).
father(jack, ray).

mother(susan, peter).	/* Susan is the mother of Peter. */
mother(susan, mary).
mother(amy, liza).
mother(amy, john).
mother(karen, susan).
mother(karen, ray).

yeye(X, Y) :- father(X, T), father(T, Y).
mama(X, Y) :- mother(X, T), father(T, Y).
gunggung(X, Y) :- father(X, T), mother(T, Y).
popo(X, Y) :- mother(X, T), mother(T, Y).