f(X, 0):-
    X < 3, !.
f(X, 1):-
    X < 6, !.
f(X, 2).
%red cut green cut

%maximum of two numbers
%without cut
max(X, Y, X):-
    X >= Y.
max(X, Y, Y):-
    X < Y.

%with cut
max_cut(X, Y, X):-
    X >= Y, !.
max_cut(X, Y, Y).

%member function with cut
member(X, [X | _ ]) :- !.

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

%add an element to an list without duplication
add(X,L,L):- member(X, L), !.
add(X, L, [X|L]).