∀ {M : Type u_1} {α : Type u_2} {β : Type u_3} [inst : MeasurableSpace α] {μ : MeasureTheory.Measure α}
  [inst_1 : TopologicalSpace β] [inst_2 : SMul M α] [inst_3 : MeasurableConstSMul M α]
  [inst_4 : MeasureTheory.SMulInvariantMeasure M α μ],
  DomMulAct.instSMulAEEqFun = { smul := fun c f => f.compMeasurePreserving (fun x => DomMulAct.mk.symm c • x) ⋯ }