i ≤ j, j ≤ 0, i ≤ 0 ⊦ i→n(i - j) = i→n(i) - i→n(j)
Used simplifier rules: forward-lele: ⊦ j ≤ j0 ∧ j0 ≤ j1 → j ≤ j1; (forward) from specification int-abs