⊦ Poton(n)(s) ↔ (∀ m. m ≤ n → Po(m)(s))
last, GInv(S), ∀ m. m ≤ n0 → Po(m)(S), Po(n0 + 1)(S), m ≤ n0 + 1, ¬ Po(m)(S) ⊦
Used terms: S, n0