proposition: Lemma gte_addl x y : x \is a fin_num -> (x + y < x) = (y < 0).
proof: Proof. by move: x y => [r| |] [s| |]// _; [rewrite !lte_fin gtrDl|rewrite !ltNyr]. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap) mathcomp(mathcomp_extra) signed