instance types.finitaryExtensive : FinitaryExtensive (Type u) := by
  classical
  rw [finitaryExtensive_iff_of_isTerminal (Type u) PUnit Types.isTerminalPunit _
      (Types.binaryCoproductColimit _ _)]
  apply BinaryCofan.isVanKampen_mk _ _ (fun X Y => Types.binaryCoproductColimit X Y) _
      fun f g => (Limits.Types.pullbackLimitCone f g).2
  · intros _ _ _ _ f hαX hαY
    constructor
    · refine' ⟨⟨hαX.symm⟩, ⟨PullbackCone.isLimitAux' _ _⟩⟩
      intro s
      

Proof state:
case h₁.left
J : Type v'
inst✝² : Category.{u', v'} J
C : Type u
inst✝¹ : Category.{v, u} C
D : Type u''
inst✝ : Category.{v'', u''} D
X Y : C
X'✝ Y'✝ : Type u
αX✝ : X'✝ ⟶ PUnit.{u + 1}
αY✝ : Y'✝ ⟶ PUnit.{u + 1}
f : (Types.binaryCoproductCocone X'✝ Y'✝).pt ⟶ (Types.binaryCoproductCocone PUnit.{u + 1} PUnit.{u + 1}).pt
hαX :
  αX✝ ≫ BinaryCofan.inl (Types.binaryCoproductCocone PUnit.{u + 1} PUnit.{u + 1}) =
    BinaryCofan.inl (Types.binaryCoproductCocone X'✝ Y'✝) ≫ f
hαY :
  αY✝ ≫ BinaryCofan.inr (Types.binaryCoproductCocone PUnit.{u + 1} PUnit.{u + 1}) =
    BinaryCofan.inr (Types.binaryCoproductCocone X'✝ Y'✝) ≫ f
s : PullbackCone f (BinaryCofan.inl (Types.binaryCoproductCocone PUnit.{u + 1} PUnit.{u + 1}))
⊢ { l //
    l ≫
          PullbackCone.fst
            (PullbackCone.mk (BinaryCofan.inl (Types.binaryCoproductCocone X'✝ Y'✝)) αX✝
              (_ :
                BinaryCofan.inl (Types.binaryCoproductCocone X'✝ Y'✝) ≫ f =
                  αX✝ ≫ BinaryCofan.inl (Types.binaryCoproductCocone PUnit.{u + 1} PUnit.{u + 1}))) =
        PullbackCone.fst s ∧
      l ≫
            PullbackCone.snd
              (PullbackCone.mk (BinaryCofan.inl (Types.binaryCoproductCocone X'✝ Y'✝)) αX✝
                (_ :
                  BinaryCofan.inl (Types.binaryCoproductCocone X'✝ Y'✝) ≫ f =
                    αX✝ ≫ BinaryCofan.inl (Types.binaryCoproductCocone PUnit.{u + 1} PUnit.{u + 1}))) =
          PullbackCone.snd s ∧
        ∀
          {m :
            s.pt ⟶
              (PullbackCone.mk (BinaryCofan.inl (Types.binaryCoproductCocone X'✝ Y'✝)) αX✝
                  (_ :
                    BinaryCofan.inl (Types.binaryCoproductCocone X'✝ Y'✝) ≫ f =
                      αX✝ ≫ BinaryCofan.inl (Types.binaryCoproductCocone PUnit.{u + 1} PUnit.{u + 1}))).pt},
          m ≫
                PullbackCone.fst
                  (PullbackCone.mk (BinaryCofan.inl (Types.binaryCoproductCocone X'✝ Y'✝)) αX✝
                    (_ :
                      BinaryCofan.inl (Types.binaryCoproductCocone X'✝ Y'✝) ≫ f =
                        αX✝ ≫ BinaryCofan.inl (Types.binaryCoproductCocone PUnit.{u + 1} PUnit.{u + 1}))) =
              PullbackCone.fst s →
            m ≫
                  PullbackCone.snd
                    (PullbackCone.mk (BinaryCofan.inl (Types.binaryCoproductCocone X'✝ Y'✝)) αX✝
                      (_ :
                        BinaryCofan.inl (Types.binaryCoproductCocone X'✝ Y'✝) ≫ f =
                          αX✝ ≫ BinaryCofan.inl (Types.binaryCoproductCocone PUnit.{u + 1} PUnit.{u + 1}))) =
                PullbackCone.snd s →
              m = l }

Next tactic:
have : ∀ x, ∃! y, s.fst x = Sum.inl y := by
        intro x
        cases' h : s.fst x with val val
        · simp only [Types.binaryCoproductCocone_pt, Functor.const_obj_obj, Sum.inl.injEq,
            exists_unique_eq']
        · apply_fun f at h
          cases ((congr_fun s.condition x).symm.trans h).trans (congr_fun hαY val : _).symm