∀ (C : Type u_2) [inst : CategoryTheory.Category.{u_1, u_2} C] {X₁ X₂ X₃ Y₁ Y₂ Y₃ : CategoryTheory.Functor C C}
  (f₁ : X₁ ⟶ Y₁) (f₂ : X₂ ⟶ Y₂) (f₃ : X₃ ⟶ Y₃),
  CategoryTheory.CategoryStruct.comp (f₁ ◫ f₂ ◫ f₃) (Y₁.associator Y₂ Y₃).hom =
    CategoryTheory.CategoryStruct.comp (X₁.associator X₂ X₃).hom (f₁ ◫ (f₂ ◫ f₃))