--------     --------
|        |   |        |     
|   1    |   |   2    |     
|        |   |        |     
|        |   |        |     
 --------     --------
 --------     --------
|        |   |        |     
|   3    |   |   4    |     
|        |   |        |     
|        |   |        |     
 --------     --------

##</code><code>##

 --------     --------
|        |   |        |     
|   1    |   |   2    |     
|        |   |        |     
|        |   |        |     
 --------     --------
 --------    
|        |      
|   3    |     empty
|        |     cell
|        |       
 --------