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