| n0 ∈ ns, ∀ 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 ∈ ns ↔ (∃ ns0. ns = ns0 ++ n ∧ ¬ n ∈ ns0)
∃ ns0. ns = ns0 ++ n0 ∧ ¬ n0 ∈ 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
Used terms: ns, n0