∀ {C : Type u_4} [inst : CategoryTheory.Category.{u_3, u_4} C] {X Y Z : C} {D : Type u_2}
  [inst_1 : CategoryTheory.Category.{u_1, u_2} D] (G : CategoryTheory.Functor C D) (f : X ⟶ Z) (g : Y ⟶ Z)
  [inst_2 : CategoryTheory.Limits.HasPullback f g],
  CategoryTheory.CategoryStruct.comp (G.map (CategoryTheory.Limits.pullback.fst f g)) (G.map f) =
    CategoryTheory.CategoryStruct.comp (G.map (CategoryTheory.Limits.pullback.snd f g)) (G.map g)