∀ {α : Type u_1} {β : Type u_2} [inst : MeasurableSpace α] {s : Set α} (hs : MeasurableSet s)
  (f g : MeasureTheory.SimpleFunc α β) (a : α),
  (MeasureTheory.SimpleFunc.piecewise s hs f g) a = if a ∈ s then f a else g a