∀ {C : Type u_1} [inst : CategoryTheory.Category.{v_1, u_1} C] {X : ℕ → C} (f : (n : ℕ) → X n ⟶ X (n + 1)) (i j : ℕ)
  (h : i = j),
  f i =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.eqToHom ⋯)
      (CategoryTheory.CategoryStruct.comp (f j) (CategoryTheory.eqToHom ⋯))