new (C → F) → (E ∧ D → ((E → D) → ((D → A) → (C → (((C ∨ F) ∧ D) ∧ ((E ∨ (D → E)) ∨ E)) ∧ E))))
intro
intro
cases 1
intro
intro
intro
cases 1
constructor
constructor
constructor
left
exact 6
exact 3
left
left
exact 2
exact 2