proposition: Lemma pmule_rgt0 x y : 0 < x -> (x * y > 0) = (y > 0).
proof: Proof. by move=> xgt0; rewrite -oppe_lt0 -muleN pmule_rlt0 ?oppe_lt0. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap) mathcomp(mathcomp_extra) signed