proposition: Lemma lerBrDl x y z : (x <= y - z) = (z + x <= y).
proof: Proof. by rewrite lerBrDr 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)