parent_of(bill, jim).
parent_of(jane, jim).
parent_of(bill, albert).
parent_of(jane, albert).

parent_of(jim, alice).
parent_of(jane, alice).
parent_of(jim, fred).
parent_of(jane, fred).
parent_of(jim, john).
parent_of(jane, john).

male(bill).
male(jim).
male(albert).
male(fred).
male(john).

male(X):- \+female(X).

female(jane).
female(alice).

father_of(F, Ch):-
	parent_of(F, Ch), male(F).

grandfather_of(Gf, Gc):-
	parent_of(Gf, Ch), parent_of(Ch, Gc), male(Gf).

brother_of(B, Sib):-
	parent_of(P, B), parent_of(P, Sib), male(B), B\==Sib.

sister_of(S, Sib):-
	parent_of(P, S), parent_of(P, Sib), female(S), S\==Sib.

