proposition: Lemma rsym_invset_trans s : transitive (rsymrel (invset s)).
proof: Proof. exact: rsymrel_trans (invsetP s). Qed.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(fingroup perm morphism presentation) mathcomp(ssralg poly ssrint) permcomp tools permuted combclass congr