proposition: Lemma pmulrz_llt0 x n (n0 : 0 < n) : x *~ n < 0 = (x < 0).
proof: Proof. by rewrite -(mul0rz _ n) ltr_pMz2r // mul0rz. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)