proposition: Lemma ltrBrDr x y z : (x < y - z) = (x + z < y).
proof: Proof. by rewrite (monoLR (addrNK _) (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)