∀ {α : Type u_1} {m0 : MeasurableSpace α} {μ : MeasureTheory.Measure α} {f : α → ENNReal},
  AEMeasurable f μ →
    ∀ {g : α → ENNReal},
      AEMeasurable g (μ.withDensity f) →
        ∀ {s : Set α}, MeasurableSet s → ∫⁻ (a : α) in s, g a ∂μ.withDensity f = ∫⁻ (a : α) in s, (f * g) a ∂μ