new C ∧ A → (((B → D) → A) → (A ∧ B → (D → (A → B) ∧ (C → A))))
intro
cases 0
intro
intro
cases 4
cases 0
cases 4
intro
cases 0
cases 4
constructor
intro
cases 0
cases 4
exact 6
intro
cases 0
cases 4
exact 2