proposition: Lemma dadde_le0 x y : x <= 0 -> y <= 0 -> x + y <= 0.
proof: Proof. rewrite dual_addeE oppe_le0 -!oppe_ge0; exact: adde_ge0. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap) mathcomp(mathcomp_extra) signed