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