proposition: Lemma nmulrz_rgt0 x n (x0 : x < 0) : 0 < x *~ n = (n < 0).
proof: Proof. by rewrite -(mulr0z x) ltr_nMz2l. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)