proposition: Lemma lerBrDr x y z : (x <= y - z) = (x + z <= y).
proof: Proof. by rewrite (monoLR (addrNK _) (lerD2r _)). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)