∀ {α : Type u_2} {C : Set (Set α)} {G : Type u_1} [inst : AddCommMonoid G] (m : Set α → G),
  MeasureTheory.IsSetRing C →
    m ∅ = 0 →
      (∀ {s t : Set α}, s ∈ C → t ∈ C → Disjoint s t → m (s ∪ t) = m s + m t) →
        ∀ (I : Finset (Set α)), ↑I ⊆ C → (↑I).PairwiseDisjoint id → ⋃₀ ↑I ∈ C → m (⋃₀ ↑I) = ∑ u ∈ I, m u