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