proposition: Lemma perm_inj {s} : injective s.
proof: Proof. by rewrite -!pvalE; apply: (injectiveP _ (valP s)). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(fingroup morphism)