proposition: Lemma tpermK x y : involutive (tperm x y).
proof: Proof. by move=> z; rewrite !permE tperm_proof. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(fingroup morphism)