% intersection(A, B, C) where C is the intersection of A and B

intersection([], _, []).
intersection([X|R], Y, [X|Z]) :-
	member(X, Y),
	intersection(R, Y, Z).
intersection([X|R], Y, Z) :-
	\+ member(X, Y),
	intersection(R, Y, Z).


% union(A, B, C) where C is the union of A and B

union([], X, X).
union([X|R], Y, Z) :-
	member(X, Y),
	union(R, Y, Z).
union([X|R], Y, [X|Z]) :-
	\+ member(X, Y),
	union(R, Y, Z).

member(X, [X|_]).
member(X, [_|Y]) :- member(X, Y).