n→i(m) = i0 + 1, i < 2 ^ i1 * 2, 2 ^ i1 ≤ i, 0 ≤ i1, 0 < 2 ^ i1, 0 < i ⊦ i = 0, # int2bits(i) ≤ m ↔ ¬ 2 ^ i0 ≤ i