j * i = j * i0 + j0, j * i ≤ j * i0 + j0, j0 < j, i0 < i, 0 ≤ j0, 0 < j ⊦
j * i ≤ j * i0 + j0, j0 < j, i0 < i, 0 ≤ j0, 0 < j ⊦ j * i = j * i0 + j0
Used formulas: j * i = j * i0 + j0