Логическое программирование (Prolog) / Практика 2 / код Подмножества

domains
list=integer*
predicates
nondeterm member(integer, list)
nondeterm subset(list, list)
nondeterm delete(integer, list, list)

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

subset([],_).
subset([X|Xs],Y):- member(X,Y), delete(X,Y,Z), subset(Xs, Z).

delete(X,[X|Ys],Ys):- !.
delete(X,[_|Ys],Z):- delete(X,Ys,Z).

goal
%subset([3,5,6],[1,2,3,4,5,6]).
subset(R,[1,2,3,4,5,6]).