proposition: Lemma tpermP x y z : tperm_spec x y z (tperm x y z).
proof: Proof. by rewrite permE /=; do 2?[case: eqP => /=]; constructor; auto. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(fingroup morphism)