proposition: Lemma normrEsign x : `|x| = (-1) ^+ (x < 0)%R * x.
proof: Proof. by rewrite -real_normrEsign. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)