>   Instead of:
> 
>     <xsl:variable name="bauteil_test">
>       <xsl:for-each select="/...//bauteil_id">
>         <xsl:if test="string(.) = string($wand_ID)">
>           <xsl:text>true</xsl:text>
>         </xsl:if>
>       </xsl:for-each>
>     </xsl:variable>
> 
> use:
> 
>     <xsl:variable name="bauteil_test">
>       <xsl:if select="/...//bauteil_id[. = $wand_ID]">
>         <xsl:text>true</xsl:text>
>       </xsl:if>
>     </xsl:variable>
> 

or better still:

<xsl:variable name="bauteil_test" select="boolean(/...//bauteil_id[. =
$wand_ID])"/>

(You can then convert the boolean to the string "true" using string() if you
want, but why not leave it as a boolean?)

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