∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] [inst_1 : CategoryTheory.Regular C] {A B : C} (f : A ⟶ B)
  (A' : CategoryTheory.Subobject A) (B' : CategoryTheory.Subobject B),
  CategoryTheory.CategoryStruct.comp
      (CategoryTheory.CategoryStruct.comp
        ((A' ⊓ (CategoryTheory.Subobject.pullback f).obj B').ofLE ((CategoryTheory.Subobject.pullback f).obj B') ⋯)
        (CategoryTheory.Subobject.pullbackπ f B'))
      B'.arrow =
    CategoryTheory.CategoryStruct.comp
      (CategoryTheory.CategoryStruct.comp ((A' ⊓ (CategoryTheory.Subobject.pullback f).obj B').ofLE A' ⋯)
        (CategoryTheory.Subobject.imageFactorisation f A').F.e)
      ((CategoryTheory.Subobject.exists f).obj A').arrow