boy(X).
girl(X).

parent(X,Y).
mother(X,Y) :- girl(X), parent(X,Y).
father(X,Y) :- boy(X), parent(X,Y).

child(X,Y) :- parent(Y,X).
daugther(X,Y) :- girl(X), child(X,Y).
son(X,Y) :- boy(X), child(X,Y).

sibling(X,Y) :- parent(Z,X), parent(Z,Y).
sister(X,Y):- girl(X), sibling(X,Y).
brother(X,Y):- boy(X), sibling(X,Y).