// ancestors parentof("douglas", "john"). parentof("john", "bob"). parentof("bob", "ebbon"). parentof("douglas", "jane"). parentof("jane", "jan"). ancestorof(A, B) <- parentof(A, B). ancestorof(A, C) <- ancestorof(A, B), parentof(B,C). grandparentof(A, B) <- parentof(A, C), parentof(C, B). cousins(A,B) <- grandparentof(C,A), grandparentof(C,B). parentof[`arg](A, B) -> int[32](A), !string(B).