| j * (j + 1) = i0 * 2 + j0, 0 < j, i0 < j, j0 < 2, j * (j + 1) < (i0 + 1) * 2, 0 ≤ j0, 0 ≤ i0, 0 ≤ j ⊦ j = 0, j * (j + 1) < j * (i0 + 1) |
⊦ i * j = j * i
j * (j + 1) = i0 * 2 + j0, j * (j + 1) < (i0 + 1) * 2, j0 < 2, i0 < j, 0 < j, 0 ≤ j, 0 ≤ i0, 0 ≤ j0 ⊦ j = 0, j * (j + 1) < (i0 + 1) * j
Used terms: i0 + 1, j