∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] {X Y : C} (f : X ⟶ Y)
  [inst_1 : CategoryTheory.Limits.HasPullbacksAlong f] (g : CategoryTheory.Over Y),
  ((CategoryTheory.Over.pullback f).obj g).left = CategoryTheory.Limits.pullback g.hom f