Xsl problem to find correct nodes using idrefs

[BadKarma]

Hi, I have a simple xml-structure to represent my bookcase.

lib
 + books
   + serie
     + book (aut: type = IDREFS)
       - title
       - pages
 + authors
   + author (id: type = ID)
     - first_name
     - last_name

It contains 2 tables, one of the authors identified with id. And a table with the books with an attribute aut pointing to one or more of the authors. Now i want to show the series, the booktitle and the author(s). The problems is how to show the author and not just the ID in the aut attribute. I have used a named template to find the author

<xsl:template name="author_name">
  <xsl:param name="idref"/>
  <xsl:for-each select="//author[@id=$idref]">
    <xsl:value-of select="last_name"/> 
    <xsl:value-of select="first_name"/>
  </xsl:for-each>
</xsl:template>

And I'm using it like this

<xsl:call-template name="author_name">
  <xsl:with-param name="idref" select="@aut"/>
</xsl:call-template>

And this works, BUT NOT for books written by 2 or more authors. I have tried tokenize but that function is only available in xls 2.0. And then IE has troubles with it. Any help on this would be appreciated.

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