0 ≤ i, 0 ≤ j ⊦ i→n(i) < i→n(j) ↔ abs(i) < abs(j)
⊦ i→n(i) < i→n(j) ↔ abs(i) < abs(j), 0 ≤ i ∧ 0 ≤ j
Used terms: i, j