| (i0 + j0) * (i0 + j0 + 1) = i1 * 2 + j1, i2 = i1 + (j0 - j), (i + j) * (i + j + 1) = i2 * 2 + j2, 0 ≤ i2, 0 ≤ j2, j1 < 2, 0 ≤ i, 0 ≤ j, 0 ≤ i0, 0 ≤ j0, 0 ≤ j1, 0 ≤ i1, j2 < 2 ⊦ i = i0 ∧ j = j0 |
(i0 + j0) * (i0 + j0 + 1) = i1 * 2 + j1, (i + j) * (i + j + 1) = (i1 + (j0 - j)) * 2 + j2, 0 ≤ i1 + (j0 - j), 0 ≤ j2, j1 < 2, 0 ≤ i, 0 ≤ j, 0 ≤ i0, 0 ≤ j0, 0 ≤ j1, 0 ≤ i1, j2 < 2 ⊦ i = i0 ∧ j = j0