∀ {α : Type u_1} {C : Set (Set α)} {m : MeasureTheory.AddContent ENNReal C},
  MeasureTheory.IsSetSemiring C →
    m.IsSigmaSubadditive →
      ∀ (f : ℕ → Set α),
        (∀ (i : ℕ), f i ∈ C) → ⋃ i, f i ∈ C → Pairwise (Function.onFun Disjoint f) → m (⋃ i, f i) = ∑' (i : ℕ), m (f i)