proposition: Lemma real_lerNnormlW x y : x \is real -> `|x| <= y -> - y <= x.
proof: Proof. by move=> ?; case/real_ler_normlP => //; rewrite lerNl. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)