⊦ bag = bag2 ↔ (∀ n. count(n, bag) = count(n, bag2))
bag -- n = ∅ ⊦ count(n0, bag) = 0, ∀ n0. count(n0, bag) = count(n0, ∅ ++ n)
Used terms: ∅ ++ n, bag