∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] {X Y Z : CategoryTheory.Limits.FormalCoproduct C} (f : X ⟶ Z)
  (g : Y ⟶ Z)
  (pb :
    (i : Function.Pullback f.f g.f) →
      CategoryTheory.Limits.PullbackCone (CategoryTheory.CategoryStruct.comp (f.φ (↑i).1) (CategoryTheory.eqToHom ⋯))
        (g.φ (↑i).2))
  (i : (CategoryTheory.Limits.FormalCoproduct.pullbackCone f g pb).pt.I),
  (CategoryTheory.Limits.FormalCoproduct.pullbackCone f g pb).fst.φ i = (pb i).fst