proposition: Lemma eqr_normN x : (`|x| == - x) = (x <= 0).
proof: Proof. by rewrite ler0_def. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)