Actually, Sebastien was pretty close.
Given :
<PERSON firstname="fn1" lastname="ln1"/>
<PERSON firstname="fn2" lastname="ln2"/>
<PERSON firstname="fn3" lastname="ln3"/>
<PERSON firstname="fn2" lastname="ln2"/>
<PERSON firstname="fn3" lastname="ln3"/>
<PERSON firstname="fn4" lastname="ln4"/>
<PERSON firstname="fn3" lastname="ln3"/>

This worked properly in XT:
  <xsl:for-each
     select="PERSON[following-sibling::PERSON/@lastname = ./@lastname
                            and following-sibling::PERSON/@firstname =
./@firstname
                     and not(preceding-sibling::PERSON/@lastname =
./@lastname
                            and preceding-sibling::PERSON/@firstname =
./@firstname)] ">
    <xsl:copy-of select="."/>
  </xsl:for-each>

It always gets the oldest brother :)

Nikita Ogievetsky
http://www.cogx.com



 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list