proposition: Lemma all_allLtn_cat (s0 s1 s : seq T) : all (allLtn (s0 ++ s1)) s -> all (allLtn s0) s /\ all (allLtn s1) s.
proof: Proof. Proof using. rewrite (eq_all (a2 := predI (allLtn s0) (allLtn s1))); first last. by rewrite /allLtn => i /=; rewrite all_cat. by rewrite all_predI => /andP[]. Qed.
imports: HB(structures) mathcomp(all_ssreflect) tools partition skewpart Yamanouchi ordtype tableau std stdtab