proposition: Lemma commr_prod (I : Type) (s : seq I) (P : pred I) (F : I -> R) x : (forall i, P i -> comm x (F i)) -> comm x (\prod_(i <- s | P i) F i).
proof: Proof. exact: (big_ind _ (commr1 x) (@commrM x)). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)