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