Removing duplicates where duplicates are determined by

Hi, consider the following problem:

-i have this sorted list of names
-I want to remove duplicates shown as the concatination of <surname> and
<first_name>

My question is:
Can anyone tell me what is wrong with my XSLT(se below)?
I hope you can help me.
The subject of removing duplicates have been discussed before, but I have not
found issues around the combination of duplicates and concatination.
I am using XMLSpy 2007 rel3.

GeirrP

Sorted list:
<?xml version="1.0" encoding="UTF-8"?>
<persons>
<person>
<surname>Per</surname><first_name>Hansen</first_name>
</person>
<person>
<surname>Per</surname><first_name>Hansen</first_name>
</person><person>
<surname>Per</surname><first_name>Olsen</first_name>
</person><person>
<surname>Jan</surname><first_name>Hansen</first_name>
</person><person>
<surname>Jan</surname><first_name>Hansen</first_name>
</person><person>
<surname>Jan</surname><first_name>Hansen</first_name>
</person><person>
<surname>Ole</surname><first_name>Pedersen</first_name>
</person><person>
<surname>jan</surname><first_name>Fredriksen</first_name>
</person><person>
<surname>Arne</surname><first_name>Jensen</first_name>
</person>
</persons>


This is the result I want to achieve:
<?xml version="1.0" encoding="UTF-8"?>
<persons>
<person>
<surname>Per</surname><first_name>Hansen</first_name>
</person>
person>
<surname>Per</surname><first_name>Olsen</first_name>
</person><person>
<surname>Jan</surname><first_name>Hansen</first_name>
</person>
person>
<surname>Ole</surname><first_name>Pedersen</first_name>
</person><person>
<surname>jan</surname><first_name>Fredriksen</first_name>
</person><person>
<surname>Arne</surname><first_name>Jensen</first_name>
</person>
</persons>


Here is the XSLT:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:fn="http://www.w3.org/2005/xpath-functions">
                <xsl:output method="xml" version="1.0" encoding="UTF-8"
indent="yes"/>
                               <xsl:template match="/ | node() | @* |
comment() | processing-instruction()">
                               <xsl:copy>
                                               <xsl:apply-templates select="@*
| node()"/>
                               </xsl:copy>
                </xsl:template>
                <xsl:template match="/">
                               <xsl:variable name="persons">
                                               <xsl:for-each
select="//person">
                                                               <xsl:copy-of
select="."/>
                                               </xsl:for-each>
                               </xsl:variable>
                               <tbody>
                                               <xsl:for-each
select="$persons/person">
                                                               <xsl:variable
name="pos" select="position( )"/>
                                                               <xsl:if
test="$pos = 1 or concat(./first_name,./surname) !=concat(./first_name[$pos -
1],./surname[$pos - 1])">
                                                                             
 <xsl:copy-of select="."/>
                                                               </xsl:if>
                                               </xsl:for-each>
                               </tbody>
                </xsl:template>
</xsl:stylesheet>