proposition: Lemma aleph_pr12b x z : ordinalp x -> ordinalp z -> \aleph x <c cardinal z -> \aleph (osucc x) <=o z.
proof: Proof. move=> ox oz ycz. exact: (oleT (ocle (aleph_pr10b ox ycz)) (card_ord_le oz)). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)