proposition: Lemma sgz_def x : sgz x = (-1) ^+ (x < 0)%R *+ (x != 0).
proof: Proof. by rewrite /sgz; case: (_ == _); case: (_ < _). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)