∀ {α : Type u_1} {m : Set α → ENNReal} {s t : Set α},
  (∀ (u : Set α), (s ∩ u).Nonempty → (t ∩ u).Nonempty → m u = ⊤) →
    (MeasureTheory.OuterMeasure.boundedBy m) (s ∪ t) =
      (MeasureTheory.OuterMeasure.boundedBy m) s + (MeasureTheory.OuterMeasure.boundedBy m) t