∀ {α : Type u_2} {ι : Type u_6} {m0 : MeasurableSpace α} [Countable ι] (μ : ι → MeasureTheory.Measure α) (s : Set α),
  (MeasureTheory.Measure.sum μ).restrict s = MeasureTheory.Measure.sum fun i => (μ i).restrict s