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