proposition: Lemma ltrBlDr x y z : (x - y < z) = (x < z + y).
proof: Proof. by rewrite (monoLR (addrK _) (ltrD2r _)). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)