i1 < 0, i * j0 = i1 + i0 * j, 0 < j, 0 < j0 ⊦ ¬ i0 * j ≤ i * j0, j0 = 0, j = 0
¬ i0 * j ≤ i * j0, i * j0 = i1 + i0 * j, 0 < j, 0 < j0 ⊦ i1 < 0, j0 = 0, j = 0