Testing against node-set

I wanna select all rows from the second rowSet, whose
parentIDs are not equal to any row id from the first
rowSet. In this example, it'd be rows 3 and 6:

	<rowSet id="1">
		<row id="1"/>
		<row id="2"/>
	</rowSet>

	<rowSet id="2">
		<row id="3"/>
		<row id="4">
			<parentID>1</parentid>
		</row>
		<row id="5">
			<parentID>2</parentid>
		</row>
		<row id="6">
			<parentID>3</parentid>
		</row>
	</rowSet>


I'm trying the following code, but it's not working.
All rows from the second rowSet are selected.

<xsl:variable name="firstRowSet"
select="rowSet[@id=1]/row"/>
<xsl:variable name="secondRowSet"
select="rowSet[@id=2]/row"/>

<xsl:for-each
select="$secondRowSet[parentID!=$firstRowSet/@id]">
...

Any ideas?


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