proposition: Lemma nsv_nS a b: ordinalp a -> ordinalp b -> S a (osucc b) = osucc (S a b).
proof: Proof. by move => oa ob; rewrite (nsvC oa (OS_succ ob)) (nsv_Sn ob oa) (nsvC oa ob). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)