new D → (E → (A → ((D ∨ E → E) → (((E → C) ∨ C) ∧ A → (D → C) ∧ E ∨ B))))
intro
intro
intro
intro
intro
cases 4
cases 4
left
constructor
intro
cases 4
cases 5
apply 12
exact 1
exact 13
exact 1