∀ {C : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} C] {X Y Z : C} (f : Y ⟶ X) (g : Z ⟶ X)
  [inst_1 : CategoryTheory.Limits.HasPullback g f],
  CategoryTheory.Presieve.pullbackArrows f (CategoryTheory.Presieve.singleton g) =
    CategoryTheory.Presieve.singleton (CategoryTheory.Limits.pullback.snd g f)