proposition: Lemma mule_lt0_lt0 x y : x < 0 -> y < 0 -> 0 < x * y.
proof: Proof. by rewrite !lt_neqAle => /andP[? ?]/andP[*]; rewrite eq_sym mule_neq0 ?mule_le0. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap) mathcomp(mathcomp_extra) signed