∀ {C : Type u_1} [inst : CategoryTheory.Category.{v_1, u_1} C] {X Y : C} [inst_1 : CategoryTheory.Limits.HasPullbacks C]
  {U V₁ V₂ : C} (f : X ⟶ Y) (i : U ⟶ Y) (i₁ : V₁ ⟶ CategoryTheory.Limits.pullback f i)
  (i₂ : V₂ ⟶ CategoryTheory.Limits.pullback f i) [inst_2 : CategoryTheory.Limits.HasPullback i₁ i₂],
  CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackDiagonalMapIso f i i₁ i₂).hom
      (CategoryTheory.Limits.pullback.snd i₁ i₂) =
    CategoryTheory.CategoryStruct.comp
      (CategoryTheory.Limits.pullback.snd (CategoryTheory.Limits.pullback.diagonal f)
        (CategoryTheory.Limits.pullback.map
          (CategoryTheory.CategoryStruct.comp i₁ (CategoryTheory.Limits.pullback.snd f i))
          (CategoryTheory.CategoryStruct.comp i₂ (CategoryTheory.Limits.pullback.snd f i)) f f
          (CategoryTheory.CategoryStruct.comp i₁ (CategoryTheory.Limits.pullback.fst f i))
          (CategoryTheory.CategoryStruct.comp i₂ (CategoryTheory.Limits.pullback.fst f i)) i ⋯ ⋯))
      (CategoryTheory.Limits.pullback.snd
        (CategoryTheory.CategoryStruct.comp i₁ (CategoryTheory.Limits.pullback.snd f i))
        (CategoryTheory.CategoryStruct.comp i₂ (CategoryTheory.Limits.pullback.snd f i)))