⊦ ns = ns0 ↔ (∀ n. n ∈ ns ↔ n ∈ ns0)
⊦ n ∈ ns.map(fn) ↔ (∃ n0. n = fn(n0) ∧ n0 ∈ ns)
Used simplifier rules: mapset-def: ⊦ n ∈ ns.map(fn) ↔ (∃ n0. n = fn(n0) ∧ n0 ∈ ns);% ⊦ ¬ n ∈ ∅; (s) Used terms: ∅, (∅).map(fn)