∀ {α : Type u_1} {β : Type u_2} {f g : α → β} {m : MeasurableSpace α} {mβ : MeasurableSpace β} {p : α → Prop}
  {x : DecidablePred p},
  MeasurableSet {a | p a} → Measurable f → Measurable g → Measurable fun x_1 => if p x_1 then f x_1 else g x_1