0 ≤ i ⊦ i→n(i) = (* m) ↔ i = n→i(m)
i→n(2 * i) = m0 * 2 + n0, n0 < 2 ⊦ m0 = i→n(i), 0 ≤ 2 * i
2 * i = n→i(m0 * 2 + n0), n0 < 2, 0 ≤ 2 * i ⊦ m0 = i→n(i)
Used terms: m0 * 2 + n0, 2 * i