accessing previous and next element in a loop

I am producing several html page from a xml document, by iterating over a 
list of items ordered by a sort element. I was looking for a way of linking 
each of these page to the previous and the next one in the list, but i didn't 
found any way of doing this :-(
Page name are determined by item id, so as to be referenced from anywhere, so 
i can't assume first page is page1.html, second is page2.html, etc...
Has anyone an idea ?
-- 
Guillaume Rousse <rousse@xxxxxxxxxxxxxx>
GPG key http://lis.snv.jussieu.fr/~rousse/gpgkey.html

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