proposition: Lemma adde_le0 x y : x <= 0 -> y <= 0 -> x + y <= 0.
proof: Proof. move: x y => [r0||] [r1||]// ? ?; rewrite !lee_fin -(addr0 0%R); exact: lerD. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap) mathcomp(mathcomp_extra) signed