proposition: Lemma sgr_norm x : sg `|x| = (x != 0)%:R.
proof: Proof. by rewrite /sg le_gtF // normr_eq0 mulrb if_neg. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)