proposition: Lemma normr_id v : `| `|v| | = `|v|.
proof: Proof. have nz2: 2 != 0 :> R by rewrite pnatr_eq0. apply: (mulfI nz2); rewrite -{1}normr_nat -normrM mulr_natl mulr2n ger0_norm //. by rewrite -{2}normrN -normr0 -(subrr v) ler_normD. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)