Testing if a nodeset is empty

Hello All,
 I am trying to avoid certain kinds of empty tags in my xml output. Looking
at the following template, I would like to avoid an empty <chapter> tag.
Unfortunately this template does not work, it always shows the chapter tags
even if they are emtpy, what am I am doing wrong?

Thanks in advance,
Nicholas Waltham


<xsl:template match="transcal/file/section">
<xsl:variable name="a"><xsl:apply-templates select="p[@stylename='heading
1,Part']" /></xsl:variable>
<xsl:if test="$a">
<chapter>
<xsl:value-of select="$a"/>
</chapter>
</xsl:if>
</xsl:template>



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