∀ {C : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} C] [inst_1 : CategoryTheory.MonoidalCategory C] {D : Type u₂}
  [inst_2 : CategoryTheory.Category.{v₂, u₂} D] [inst_3 : CategoryTheory.MonoidalCategory.MonoidalLeftAction C D]
  (X : D), CategoryTheory.ModObj.smul = (CategoryTheory.MonoidalCategory.MonoidalLeftActionStruct.actionUnitIso X).hom