proposition: Lemma real_maxNr x : x \is real -> max (- x) x = `|x|.
proof: Proof. by move=> x_real; rewrite comparable_maxC ?real_maxrN ?real_comparable ?realN. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)