new C ∧ A → (C ∧ B → ((B ∨ D → A) → (A ∧ D → (D → (D → B)) ∨ D)))
intro
cases 0
intro
cases 3
intro
intro
cases 7
cases 0
cases 3
cases 7
left
intro
cases 0
cases 3
cases 7
intro
cases 0
cases 3
cases 7
exact 5