THIS FILE IS NOT USED FOR THE MAIN RESULT

theorem MeasurableSet.accumulate {α : Type u_1} {x✝ : MeasurableSpace α} {s : ℕ → Set α} (hs : ∀ (n : ℕ), MeasurableSet (s n)) (n : ℕ) : MeasurableSet (Set.accumulate s n)