proposition: Lemma real_normrEsign (x : R) (xR : x \is real) : `|x| = (-1) ^+ (x < 0)%R * x.
proof: Proof. by rewrite {3}[x]realEsign // signrMK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)