⊦ ns < n ↔ (∀ n0. n0 ∈ ns → n0 < n)
∀ n0. n0 = n ∨ n0 ∈ ns → ¬ n < n0 ⊦ ∀ n0. n0 ∈ ns → n0 < n + 1
Used terms: n + 1, ns