%sub(+SETA,+SETB,-SETC).
%method1
%sub([],B,[]).
%sub([H|T],B,[H|CT]):-not(member(H,B)),sub(T,B,CT).
%sub([H|T],B,CT):-member(H,B),sub(T,B,CT).

%method2
%sub(A,B,C):-subtract(A,B,C).
%
%
%
sub([],B,[]).
sub([Ha|Ta],B,[Ha|Tc]):- not(member(Ha,B)),sub(Ta,B,Tc).
sub([Ha|Ta],B,Tc):-  member(Ha,B),sub(Ta,B,Tc).