new (C ∨ F → F) → (F → ((F → E) → (D ∧ A → (F ∨ D → (((D ∨ B) ∨ D) ∧ E) ∧ E))))
intro
intro
intro
intro
cases 3
cases 3
intro
cases 3
constructor
constructor
left
left
exact 4
apply 2
exact 1
apply 2
exact 1