yes :- ab(X), !, X = b. % bad cut, red cut
yes.

ab(a).
ab(b).


% maximum relation:
max(X,Y,M) :- X >= Y, !, M = X.
max(X,Y,M) :- M = Y.

maxIf(X,Y,M) :- X >= Y -> M = X ; M = Y.
