proposition: Lemma realEsign x : x \is real -> x = (-1) ^+ (x < 0)%R * `|x|.
proof: Proof. by case/real_ge0P; rewrite (mul1r, mulN1r) ?opprK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)