A(nother) question on contrasts in SPSS

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A(nother) question on contrasts in SPSS

Andra Th
Dear list, 

I have two factors each with 3 levels. 
Say these are A (a1,a2,a3) and B (b1,b2,b3). 
I am interested to know whether a3b3 is different from all other combinations of factor levels. 
I tried, based on what I reviewed in this list and other places, to set some contrasts using /TEST in SPSS. 
For example, the difference between a3b3 and a1b1 can be written as:

mixed IS by A B  
  /fixed =  A B A*B
/TEST = 'mean diff' intercept 0 A 0 -1 1 B 0 0 0 A*B 0 0 0 0 -1 0 0 1 0.   

I've estimated the differences between a3b3 and all other combinations of levels. 
However, I am interested in knowing whether a3b3 differs from all other combinations of levels combined. How can I do this in SPSS? Do I sum or average over all the other contrasts and test the difference between a3b3 and this sum/average? I tried this but it doesn't seem to work. 
Should I be doing something different? 
Any thoughts greatly appreciated. 

Andra
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