∀ {C : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} C] {D : Type u₂} [inst_1 : CategoryTheory.Category.{v₂, u₂} D]
  {T : D} {S : CategoryTheory.Functor C D} {A B : CategoryTheory.CostructuredArrow S T} (f : A.left ⟶ B.left)
  (w : CategoryTheory.CategoryStruct.comp (S.map f) B.hom = A.hom) [h : CategoryTheory.Epi f],
  CategoryTheory.Epi (CategoryTheory.CostructuredArrow.homMk f w)