⊦ bag0 ⊆ bag1 ↔ (∀ a. count(a, bag0) ≤ count(a, bag1))
∀ a0. count(a0, bag0 ++ a) ≤ count(a0, bag1) ⊦ ∀ a. count(a, bag0) ≤ count(a, bag1)
Used terms: bag1, bag0