proposition: Lemma sgr_ge0 x : (sgr x >= 0) = (x >= 0).
proof: Proof. by rewrite !leNgt sgr_lt0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)