§ Example of Non Commuting Summation


Consider the 2D region:
|...
|1  1  1  1  1
|1  1  1  1 -1
|1  1  1 -1 -1
|1  1 -1 -1 -1
|1 -1 -1 -1 -1 ...
+---------

Ie, we have a "diamond" of 1s:
|...
|* * * * *
|* * *
|* * *
|* *
|*
+---------