proposition: Lemma ltr_nwDl y x z : x < 0 -> y <= z -> x + y < z.
proof: Proof. by move=> *; rewrite -[z]add0r ltr_leD. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)