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