proposition: Lemma card_Sym : #|Sym| = #|S|`!.
proof: Proof. by rewrite cardsE /= card_perm. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(fingroup morphism)