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