female(joy).
female(alice).
female(sue).

male(mark).
male(jim).

parents(joy, barbara, dale).
parents(mark, alicia, tyrone).
parents(alice, barbara, dale).
parents(sue, alicia, tyrone).
parents(jim, barbara, dale).

sisterof(X,Y) :-
    female(X),
    parents(X,M,F),
    parents(Y,M,F),
    X \== Y,
    write(X), write(' is a sister of '), write(Y), nl.