Xslt
From Federal Burro of Information
<xsl:stylesheet
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0">
<xsl:output method="text"/>
<xsl:template match="/">
<xsl:for-each select="db/states/state[not(@stateNumber = /db/cities/city/@stateNumber)]/@stateNumber">
<xsl:value-of select="."/>
<xsl:if test="position() != last()"><xsl:text> </xsl:text></xsl:if>
</xsl:for-each>
</xsl:template>
</xsl:stylesheet>
