∀ {C : Type u_3} [inst : CategoryTheory.Category.{u_1, u_3} C] {D : Type u_4}
  [inst_1 : CategoryTheory.Category.{u_2, u_4} D] [inst_2 : CategoryTheory.MonoidalCategory D]
  (X₁ X₂ : CategoryTheory.Functor C D),
  CategoryTheory.MonoidalCategoryStruct.tensorHom (CategoryTheory.CategoryStruct.id X₁)
      (CategoryTheory.CategoryStruct.id X₂) =
    CategoryTheory.CategoryStruct.id (CategoryTheory.MonoidalCategoryStruct.tensorObj X₁ X₂)