proposition: Lemma leeD a b x y : a <= b -> x <= y -> a + x <= b + y.
proof: Proof. move: a b x y => [a| |] [b| |] [x| |] [y| |]; rewrite ?(leey, leNye)//. by rewrite !lee_fin; exact: lerD. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap) mathcomp(mathcomp_extra) signed