proposition: Lemma ler_distl x y e : (`|x - y| <= e) = (y - e <= x <= y + e).
proof: Proof. exact: real_ler_distl. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)