:- dynamic male/1, female/1, parentOf/2, married/2

% X is a mother of Y if X is a female parent of Y
motherOf(X,Y) :- parentOf(X,Y), female(X).

% X is a father of Y if X is a male parent of Y
fatherOf(X,Y) :- parentOf(X,Y), male(X).

% X and Y are siblings if they share a parent and are different
siblings(X,Y) :- parentOf(P1,X), parentOf(P1,Y), X \= Y.

isParent(X) :- parentOf(X,_).

childLess(X) :- \+ isParent(X).

spouse(X,Y) :- married(X,Y).
spouse(X,Y) :- married(Y,X).

grandparentOf(X, GP) :- parentOf(X, P), parentOf(P, GP).

cousin(X,Y) :-
  grandparentOf(X, G),
  grandparentOf(Y,G),
  X \= Y,
  \+ siblings(X,Y).