extracting preceding nodes with certain exceptions

Hello all,
 I need some help with the following:
I have (but could be variable):
<tokens>
   <token position="1"/>
   <token position="2"/>
   <token-group>
        <row>
            <token position="3"/>
            <token posistion="4"/>
         </row>
         <row>
             <token position="5"/>
             <token position="6"/>
          </row>
    </token-group>
</tokens>

I would like to sum the values of all preceding nodes of <token> #6 that 
are <token>s, but which are not descendants of the preceding sibling of 
its ancestor <row>, that is I want to exclude <token>s #3 and #4.
I have sum(ancestor::row//token[(_at_)position &lt; $token-position]) where 
in this case $token-position = 6, but that excludes the tokens in 
positions 1 and 2.   I think I am missing something simple here, but 
suggestions are welcome.
thanks in advance,
Matthew L. Avizinis
Gleim Publications, Inc.


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