new D → (B ∨ D → (B ∧ A → ((D ∨ B → C) → (((B → E) → B) → (B ∨ C ∧ B) ∨ ((A → D ∨ E) ∨ (E ∨ D))))))
intro
intro
intro
cases 2
intro
intro
cases 2
left
left
exact 3