proposition: Lemma nmulrz_llt0 x n (n0 : n < 0) : x *~ n < 0 = (0 < x).
proof: Proof. by rewrite -(mul0rz _ n) ltr_nMz2r // mul0rz. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)