/* 1 */
unik(X, List) :- select(X, List, ListWithXRemoved), not(member(X, ListWithXRemoved)).

/* 2 */
snitt([], [], []).
snitt(_, [], []).
snitt([], _, []).
snitt([X|Xs], Y, [X|S]) :- member(X, Y), snitt(Xs, Y, S).
snitt([X|Xs], Y, S) :- not(member(X, Y)), snitt(Xs, Y, S).

/* 3 */
s1 --> [].
s1 --> [a], s, [b].

s2 --> [].
s2 --> [a], s1, [b, b].

/* 4 */
s3 --> [].
s3 --> [a, a], s1.

/* 5 */

/* 6 */
produkt(X,Y,P):- findall([A,B],(member(A,X),member(B,Y)),P).

/* 7 */
platt(X, [X]) :- not(is_list(X)).
platt([], []).
platt([X|Xs], P) :- platt(X, A), platt(Xs, B), append(A, B, P).