proposition: Lemma ord_negl_lt a b: ordinalp a -> ordinalp b -> a <<o b -> ((a = \0o /\ b = \0o) \/ (a <o b)).
proof: Proof. rewrite /ord_negl;move=> oa ob abz. move: (osum_Mle0 oa ob); rewrite abz => /ole_eqVlt; case; last by right. by move => ab; move: abz; rewrite ab => /(osum2_a_ab ob ob) -> ; left. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)