proposition: Lemma perm1 x : (1 : {perm T}) x = x.
proof: Proof. by rewrite permE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(fingroup morphism)