proposition: Lemma sgz0 : sgz (0 : R) = 0.
proof: Proof. by rewrite /sgz eqxx. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)