proposition: Lemma sgr_nat n : sg n%:R = (n != 0)%:R :> R.
proof: Proof. by rewrite sgrMn sgr1 mulr1. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)