father(Father, Child) :- man(Father), parent(Father, Child).
mother(Mother, Child) :- woman(Mother), parent(Mother, Child).

child(Child, Mother, Father) :-
             woman(Mother),
             man(Father),
             parent(Mother, Child),
             parent(Father, Child).

man(Man) :- \+ woman(Man).
woman(Woman) :- \+ man(Woman).

is_father(Father) :- father(Father, _).
is_mother(Mother) :- mother(Mother, _).
is_child(Child) :- child(Child, _, _).

man(stew).

man(jon).

woman(jess).

woman(mum).
parent(mum, jess).
parent(mum, stew).

man(dad).
parent(dad, jess).
parent(dad, stew).