proposition: Lemma ltr_wpDl y x z : 0 <= x -> y < z -> y < x + z.
proof: Proof. by move=> *; rewrite -[y]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)