new (D ∨ C → C) → ((B ∨ C → E) → ((E ∨ B → A) → (E ∧ C → (B ∨ B → ((D → D) → B)))))
intro
intro
intro
intro
cases 3
cases 3
intro
cases 3
intro
cases 3
cases 8
exact 14
exact 15