⊦ ns = ns0 ↔ (∀ n. n ∈ ns ↔ n ∈ ns0)
∀ n0. n0 ∈ below(ns, ns.min + n) ↔ n0 ∈ ∅ ⊦ # ns = 0, n = 0, ns = ∅
Used terms: ∅, below(ns, ns.min + n)