RE: counting elements with values that match other el

>     I have a set of elements ("t") with children under them 
> ("t/cSet/c").  I'm looking for children that occur twice.  
> I'd like get a nice 1.0 nodeset, which is the practical 
> reason for trying to shoehorn the task into a single statement. 

In 1.0, use keys as David Carlisle showed.

In 2.0:

<xsl:variable name="children-that-occur-twice">
  <xsl:for-each-group select="t" group-by="t/cSet/c"/>
      <xsl:sequence select="current-group()[last()=2]"/>
  </xsl:for-each-group>
</xsl:variable>

Michael Kay
http://www.saxonica.com/