proposition: Lemma mulr_sg_norm x : sg x * `|x| = x.
proof: Proof. by rewrite -numEsg. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)