proposition: Lemma sgrN1 : sg (-1) = -1 :> R.
proof: Proof. by rewrite ltr0_sg // ltrN10. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)