proposition: Lemma normrEsg x : `|x| = sg x * x.
proof: Proof. by case: sgrP; rewrite ?(mul0r, mul1r, mulN1r). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)