{ι : Type u_1} →
  {α : Type u_2} →
    {β : Type u_3} →
      [inst : MeasurableSpace α] →
        {s : ι → Set α} →
          [Finite ι] →
            IndexedPartition s →
              (∀ (i : ι), MeasurableSet (s i)) → (ι → MeasureTheory.SimpleFunc α β) → MeasureTheory.SimpleFunc α β