∀ {α : Type u_1} {β : Type u_2} {f g : α → β} {x : MeasurableSpace α} [inst : TopologicalSpace β] {p : α → Prop}
  {x_1 : DecidablePred p},
  MeasurableSet {a | p a} →
    MeasureTheory.StronglyMeasurable f →
      MeasureTheory.StronglyMeasurable g → MeasureTheory.StronglyMeasurable fun x => if p x then f x else g x