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