j < 0, i < i0, i < 0, 0 < i0, i + 1 < i0 ⊦ (i * i0) / (j * i0) = i / j, j = 0
i < i0, i < 0, 0 < i0, i + 1 < i0 ⊦ j < 0, (i * i0) / (j * i0) = i / j, j = 0
Used formulas: j < 0