I don't find a proof of the simple fact : b41 : lemma forall (x, y: real): x >=0 and y <= 1 => x * y <= x Why this lemma is not trivial in PVS ? Sincerely yours -- Michel Levy 36 rue George Sand 38400 Saint Martin d'Hères email : Michel.Levy@imag.fr http://www-lsr.imag.fr/users/Michel.Levy/