⊦ count(n, bag0 ++ n0) = (n = n0 ⊃ 1;0) + count(n, bag0)
⊦ (n0 = m ⊃ 1;0) + count(n0, bag ++ n) = count(n0, bag ++ m ++ n)
Used terms: m, bag ++ n, n0