proposition: Lemma cast_perm_id n eq_n s : cast_perm eq_n s = s :> 'S_n.
proof: Proof. by apply/permP => i; rewrite /cast_perm /= eq_axiomK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(fingroup morphism)