| ∀ ns0, n, m. # ns0 < # ns → true → (n ∈ below(ns0, m) ↔ n ∈ ns0 ∧ n < m) ⊦ # ns = 0, n ∈ below(ns, m) ↔ n ∈ ns ∧ n < m, ns = ∅ |
⊦ ns = ns0 ↔ (∀ n. n ∈ ns ↔ n ∈ ns0)
∀ ns0, n, m. # ns0 < # ns → true → (n ∈ below(ns0, m) ↔ n ∈ ns0 ∧ n < m) ⊦ # ns = 0, n ∈ below(ns, m) ↔ n ∈ ns ∧ n < m, ∀ n. n ∈ ns ↔ n ∈ ∅
Used terms: ∅, ns