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<xsl:for-each select="years/year">
<xsl:sort select="." order="descending"/>
<a href="?year={.}">
<xsl:if test="/informationsystem/year = .">
<xsl:attribute name="class">active</xsl:attribute>
</xsl:if>
<xsl:value-of select="."/></a>
</xsl:for-each>