2/*
    3
    4Somehow these still appeared in operations.pl file
    5
    6subset([],_).
    7subset([E|Sub],Set):-member(E,Set),!,subset(Sub,Set).
    8
    9intersection([],_,[]).
   10intersection([H|L1],L2,[H|L3]):-member(H,L2),!,
   11	intersection(L1,L2,L3).
   12 intersection([_|L1],L2,L3):-intersection(L1,L2,L3).
   13
   14flatten([],[]):-!.
   15flatten([[]|T],Res):-!,flatten(T,Res).
   16flatten([[H1|T1]|T],Res):-!,flatten(T,Res1),!,
   17	append([H1|T1],Res1,Res).
   18flatten([H|T],[H|Res]):-!,flatten(T,Res).
   19*/