⊦ unique-elems(bag) ↔ (∀ n. count(n, bag) ≤ 1)
⊦ (∀ n. count(n, bag ++ m) ≤ 1) ↔ (∀ n. count(n, bag) ≤ 1) ∧ ¬ m ∈ bag
Used terms: bag