<xsl:template match="sort">
<table>
<xsl:for-each select='person/city[not(preceding::person/city=.)]'>
	<xsl:sort/>
	<tr>
		<td><xsl:value-of select='.'/></td>

		<xsl:for-each select='ancestor::sort/person[city=current()]'>
			<xsl:sort/>
			<td><xsl:value-of select='name'/></td>
		</xsl:for-each>
	</tr>
</xsl:for-each>
</table>
</xsl:template>

<sort>
	<person><name>Fabien</name>	<city>Antibes</city></person>
	<person><name>Patrick</name>	<city>Nice</city></person>
	<person><name>Olivier</name>	<city>Auribeau</city></person>
	<person><name>Alain</name>	<city>Antibes</city></person>
</sort>