 &quot;A&quot;           | &quot;u&quot;           |
| &quot;u&quot;           | &quot;A&quot;           |
| &quot;u&quot;           | &quot;u&quot;           |
o---------------o---------------o
| &quot;B&quot;           | &quot;B&quot;           |
| &quot;B&quot;           | &quot;i&quot;           |
| &quot;i&quot;           | &quot;B&quot;           |
| &quot;i&quot;           | &quot;i&quot;           |
o---------------o---------------o

Or, for those who prefer a visual representation: 

|             