proposition: Lemma tpermD x y z : x != z -> y != z -> tperm x y z = z.
proof: Proof. by case: tpermP => // ->; rewrite eqxx. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(fingroup morphism)