proposition: Lemma normr_prod I r (P : pred I) (F : I -> R) : `|\prod_(i <- r | P i) F i| = \prod_(i <- r | P i) `|F i|.
proof: Proof. exact: (big_morph norm normrM normr1). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)