proposition: Lemma sgz_eq0 x : (sgz x == 0) = (x == 0).
proof: Proof. by rewrite sgz_cp0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)