proposition: Lemma imset_perm1 (S : {set T}) : [set (1 : {perm T}) x | x in S] = S.
proof: Proof. apply: im_perm_on; exact: perm_on1. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(fingroup morphism)