∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] {X Y : C} (f : X ⟶ Y)
  [inst_1 : CategoryTheory.IsSplitEpi f],
  CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.id X) f =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp f (CategoryTheory.section_ f)) f