∀ {C₁ : Type u₁} {C₂ : Type u₂} {C₃ : Type u₃} [inst : CategoryTheory.Category.{v₁, u₁} C₁]
  [inst_1 : CategoryTheory.Category.{v₂, u₂} C₂] [inst_2 : CategoryTheory.Category.{v₃, u₃} C₃]
  {G : CategoryTheory.Functor C₁ᵒᵖ (CategoryTheory.Functor C₃ C₂)} {f₁ f₁' : CategoryTheory.Arrow C₁}
  {f₃ : CategoryTheory.Arrow C₃} (sq₁₃ : G.PullbackObjObj f₁.hom f₃.hom) (sq₁₃' : G.PullbackObjObj f₁'.hom f₃.hom)
  (sq : f₁' ⟶ f₁), (sq₁₃.mapArrowLeft sq₁₃' sq).left = (G.map sq.right.op).app f₃.left