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