∀ {𝕜 : Type u_1} {ι : Type u_2} [inst : Fintype ι] [inst_1 : RCLike 𝕜] {E : ι → Type u_3} (f : (i : ι) → E i → 𝕜)
  {mE : (i : ι) → MeasurableSpace (E i)} {μ : (i : ι) → MeasureTheory.Measure (E i)}
  [∀ (i : ι), MeasureTheory.SigmaFinite (μ i)],
  ∏ i, ∫ (x : E i), f i x ∂μ i = ∫ (x : (i : ι) → E i), ∏ i, f i (x i) ∂MeasureTheory.Measure.pi μ