i + j < 0 ⊦ 0 = (abs(i) + abs(j)) + i + j, 0 < j, 0 < i
Used simplifier rules: Abs-neg: ⊦ j < 0 → abs(j) = 0 - j;%sub-eq: ⊦ i - j = i0 ↔ i = i0 + j;