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