new C → (A → ((C → B) → ((B ∨ E → B) → (A → (B ∧ (F ∧ ((B ∨ E) ∨ A)) → B ∨ (E → B ∧ E))))))
intro
intro
intro
intro
intro
intro
cases 5
cases 5
cases 7
cases 9
left
exact 6