father(caroline, john).

father(johnJr, john).

father(john, joe).

father(fred, johnJr).

grandfath(X, Y) :- father(X, Z), father(Z, Y).


anc(X, Y) :- father(X, Y).

anc(X, Y) :- father(X, Z), anc(Z, Y).


setof1(X, G, Z) :- setof(X, G, Z) -> true ; Z = [].

% member function, non-built-in version

m(X, [X | _]).

m(X, [ _ | L]) :- m(X, L).


% set intersection

int(X, Y, Z) :- setof(A, (m(A, X), m(A, Y)), Z).


% Using bagof instead of setof

bagint(X, Y, Z) :- bagof(A, (m(A, X), m(A, Y)), Z).