∀ {ι : Type u_1} [inst : Fintype ι] {β : Option ι → Type u_4} [inst_1 : (i : Option ι) → MeasurableSpace (β i)]
  (μ : (i : Option ι) → MeasureTheory.Measure (β i)) [∀ (i : Option ι), MeasureTheory.SigmaFinite (μ i)],
  MeasureTheory.Measure.map (⇑(MeasurableEquiv.piOptionEquivProd β).symm)
      ((MeasureTheory.Measure.pi fun i => μ (some i)).prod (μ none)) =
    MeasureTheory.Measure.pi μ