⊦ bag = bag2 ↔ (∀ n. count(n, bag) = count(n, bag2))
∀ n0. count(n0, bag -- n) = count(n0, ∅) ⊦ count(n0, bag) = 0, count(n1, bag) = count(n1, ∅ ++ n)
Used terms: ∅, bag -- n