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Example

Arithmetic modulo 3:

+3	-4	-3	-2	-1	0	1	2	3	4
-4	1	2	0	1	2	0	1	2	0
-3	2	0	1	2	0	1	2	0	1
-2	0	1	2	0	1	2	0	1	2
-1	1	2	0	1	2	0	1	2	0
0	2	0	1	2	0	1	2	0	1
1	0	1	2	0	1	2	0	1	2
2	1	2	0	1	2	0	1	2	0
3	2	0	1	2	0	1	2	0	1
4	0	1	2	0	1	2	0	1	2

   

*3	-4	-3	-2	-1	0	1	2	3	4
-4	1	0	2	1	0	2	1	0	2
-3	0	0	0	0	0	0	0	0	0
-2	2	0	1	2	0	1	2	0	1
-1	1	0	2	1	0	2	1	0	2
0	0	0	0	0	0	0	0	0	0
1	2	0	1	2	0	1	2	0	1
2	1	0	2	1	0	2	1	0	2
3	0	0	0	0	0	0	0	0	0
4	2	0	1	2	0	1	2	0	1

Same pattern is repeated every 3 lines and every 3 columns.