proposition: Lemma sgr0 : sg 0 = 0 :> R.
proof: Proof. by rewrite /sgr eqxx. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)