new A ∨ (C ∨ C) → (C ∧ D → (A ∧ D → (B ∧ C → (D ∧ (D ∧ A)) ∧ ((D → A) → C) ∨ (D ∨ B))))
intro
intro
cases 1
intro
cases 4
intro
cases 7
cases 1
cases 4
cases 7
left
constructor
constructor
exact 3
constructor
exact 3
exact 5
intro
cases 1
cases 4
cases 7
exact 2