∀ {α : Type u_3} {E : Type u_1} {m : MeasurableSpace α} {p : ENNReal} {μ : MeasureTheory.Measure α}
  [inst : NormedAddCommGroup E] {β : Type u_2} [inst_1 : MeasurableSpace β] {μb : MeasureTheory.Measure β} (f : α → β)
  (hf : MeasureTheory.MeasurePreserving f μ μb) (x y : ↥(MeasureTheory.Lp E p μb)),
  (↑(MeasureTheory.Lp.compMeasurePreserving f hf)).toFun (x + y) =
    (↑(MeasureTheory.Lp.compMeasurePreserving f hf)).toFun x + (↑(MeasureTheory.Lp.compMeasurePreserving f hf)).toFun y