| ∀ a0. (a0 = b ⊃ 1;0) + count(a0, bag0) = count(a0, bag1) ⊦ bag0 ++ b = bag1 |
⊦ bag0 = bag1 ↔ (∀ a. count(a, bag0) = count(a, bag1))
∀ a0. (a0 = b ⊃ 1;0) + count(a0, bag0) = count(a0, bag1) ⊦ ∀ a. count(a, bag0 ++ b) = count(a, bag1)
Used terms: bag1, bag0 ++ b