+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|   |         u   t     |   |   |         d   c   b     | 1   0 |
+   +   +---+   +   +---+   +   +---+---+   +---+   +---+   +---+
|           | v | s   r   q   p   o   n | e   f | a   9 | 2   3 |
+   +---+---+   +---+---+---+   +---+   +---+   +---+   +---+   +
|           | w   x   y |           | m | h   g |     8 | 5   4 |
+   +---+   +---+---+   +   +---+---+   +   +---+---+   +   +---+
|       |   |   |10   z |       |     l | i         | 7   6     |
+   +   +   +   +   +---+---+   +   +   +   +   +   +   +   +---+
|   |   |       |11  12 |       |   | k   j |   |   |   |   |   |
+   +---+---+   +---+   +   +---+   +   +---+   +---+---+   +   +
|   |       |   |14  13 |       |   |       |           |       |
+   +   +   +   +   +---+---+   +---+---+   +   +   +---+---+---+
|   |   |       |15 |       |   |       |   |   |   |1i  1j     |
+   +   +---+---+   +   +   +   +   +   +---+   +---+   +   +   +
|   |       |   |16 |   |       |   |           |1g  1h |1k |   |
+   +---+---+   +   +---+---+---+---+---+---+---+   +---+   +---+
|               |17  18  19  1a  1b  1c  1d  1e  1f |1m  1l     |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+