Re: how to do set operations (intersection, unify, re

the set operations, union etx work on sequences of nodes, using node
identity so are nit what you want here as you have sequences of strings.

Yor description is not at all clear, but if you have two sequences of
strings $a and $b and want 

the sequence of strings common to both then
that is
$a[.=$b]

the sequence of strings in $a but not in $b is

$a[not(.=$b)]

David

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