∀ {α : Type u_1} [ms : MeasurableSpace α] (m : MeasureTheory.OuterMeasure α),
  ms ≤ m.caratheodory →
    ∀ (_f : ℕ → Set α),
      (∀ (i : ℕ), MeasurableSet (_f i)) → Pairwise (Function.onFun Disjoint _f) → m (⋃ i, _f i) = ∑' (i : ℕ), m (_f i)