∀ {ι : Type u_1} {M : Type u_4} [inst : CommMonoid M] (s : Finset ι) (p : ι → Prop) [inst_1 : DecidablePred p]
  [inst_2 : (x : ι) → Decidable ¬p x] (f : ι → M), (∏ x ∈ s with ¬p x, f x) * ∏ x ∈ s with p x, f x = ∏ x ∈ s, f x