proposition: Lemma normr_sign s : `|(-1) ^+ s : R| = 1.
proof: Proof. by rewrite normrX normrN1 expr1n. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)