proposition: Lemma perm_proof (f : T -> T) : injective f -> injectiveb (finfun f).
proof: Proof. by move=> f_inj; apply/injectiveP; apply: eq_inj f_inj _ => x; rewrite ffunE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(fingroup morphism)