proposition: Lemma realNEsign x : x \is real -> - x = (-1) ^+ (0 < x)%R * `|x|.
proof: Proof. by move=> Rx; rewrite -normrN -oppr_lt0 -realEsign ?rpredN. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)