a1 | a2 | a3 | d | |
x1 | 2 | 0 | 0 | 0 |
x2 | 0 | 1 | 0 | 1 |
x3 | 1 | 0 | 1 | 0 |
x4 | 2 | 0 | 0 | 1 |
x5 | 2 | 0 | 1 | 1 |
x6 | 0 | 1 | 1 | 1 |