∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] {X Y : C} {f g : X ⟶ Y}
  {c : CategoryTheory.Limits.Fork f g} {Z : C} (h : Y ⟶ Z),
  CategoryTheory.CategoryStruct.comp c.ι (CategoryTheory.CategoryStruct.comp f h) =
    CategoryTheory.CategoryStruct.comp c.ι (CategoryTheory.CategoryStruct.comp g h)