proposition: Lemma max_nf : forall a b, nf a -> nf b -> nf (max a b).
proof: Proof. intros c c'; case (max_dec c c'); intro H;rewrite H;auto. Qed.
imports: Arith Omega Compare_dec Relations Wellfounded Tools More_nat Wf_nat AccP not_decreasing ArithRing term rpo List