Re: Question on Kaysian method for set intersection

I used Kaysian method as described in this document (section 1c), sofar:
http://www.xml.org//sites/www.xml.org/files/xslt_efficient_programming_techniques.pdf#page=3

Now I wanted to use it similarly for nodesets from different parts of
document.
That does not work because /flags[1]/flag[.='A'] is not the same node
as /flags[2]/flag[.='A'].
Is it possible to get the flag with "A" for $int and flags for "A", "B" and
"C" for $uni?
If so, with keys?

Michael Kay
Saxonica