proposition: Lemma inj_tperm (T T' : finType) (f : T -> T') x y z : injective f -> f (tperm x y z) = tperm (f x) (f y) (f z).
proof: Proof. by move=> injf; rewrite !permE /= !(inj_eq injf) !(fun_if f). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(fingroup morphism)