∀ {α : Type u_1} {β : Type u_2} {γ : Type u_3} [inst : MeasurableSpace α] (f : MeasureTheory.SimpleFunc α β) (g : β → γ)
  (s : Set γ), ⇑(MeasureTheory.SimpleFunc.map g f) ⁻¹' s = ⇑f ⁻¹' ↑({b ∈ f.range | g b ∈ s})