male(john).
male(jack).
male(peter).
male(sam).

female(mary).
female(linda).
female(lisa).
female(susan).

parent(john, jack).
parent(john, linda).
parent(mary, jack).
parent(mary, linda).
parent(jack, sam).
parent(lisa, sam).
parent(peter, susan).
parent(susan, linda).

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

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

sibling(X, Y) :- parent(P, X), parent(P, Y), X \= Y.

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

grandchild(X, Y) :- grandparent(Y, X).

uncle_or_aunt(X, Y) :- sibling(X, Z), parent(Z, Y).

cousin(X, Y) :- parent(P1, X), parent(P2, Y), sibling(P1, P2).