| count(a, bag1) = 0 ⊦ (count(a0, bag1) ≤ count(a0, bag0 ++ a) ⊃ count(a0, bag0 ++ a) - count(a0, bag1);0) = count(a0, (bag0 \ bag1) ++ a) |
count(a0, bag1) ≤ count(a0, bag0 ++ a), count(a, bag1) = 0 ⊦ count(a0, bag0 ++ a) - count(a0, bag1) = count(a0, (bag0 \ bag1) ++ a)
¬ count(a0, bag1) ≤ count(a0, bag0 ++ a), count(a, bag1) = 0 ⊦ 0 = count(a0, (bag0 \ bag1) ++ a)