parent(cyrill, renaud). parent(cyrill, claire). parent(renaud, clovis). parent(valentin, olivier). parent(claire, olivier). parent(renaud, claudia). parent(claire, gaelle). brothersister(X,Y) <-- parent(Z,X), parent(Z,Y). grandparent(X,Y) <-- parent(X,Z), parent(Z,Y). cousin(X,Y) <-- grandparent(Z,X), grandparent(Z,Y). ancester(X,Y) <-- parent(X,Y). ancester(X,Y) <-- grandparent(X,Y).