| ∀ a0. count(a0, bag0 ++ a) ≤ count(a0, bag1) ⊦ count(a, bag1) = 0, count(a0, bag0) ≤ count(a0, bag1) - (a0 = a ⊃ 1;0) |
a0 = a, ∀ a0. count(a0, bag0 ++ a) ≤ count(a0, bag1) ⊦ count(a, bag1) = 0, count(a0, bag0) ≤ count(a0, bag1) - 1
∀ a0. count(a0, bag0 ++ a) ≤ count(a0, bag1) ⊦ a0 = a, count(a, bag1) = 0, count(a0, bag0) ≤ count(a0, bag1) - 0