regarding unique nodes in a nodelist-variable

Hello all,
This is regarding the sorting on unique nodes. I am using the axis method to
sort it.
eg..
not( parent/child = preceding-sibling::parent/child)

now if i have to go through a nodelist and sort.. can i use the same thing?
like
<xsl:for-each
select="xalan:nodeset($MyElementSet)/elements/element[not(parent/childelemen
t = preceding-sibling::element/parent/childelement)]/>

The structure of the xml in the variable:

<elements>
 <element>
   <parent>
    <childelement>child1</childelement>
   <parent>
 </element>
<element>
   <parent>
    <childelement>child2</childelement>
   <parent>
 </element>
<element>
   <parent>
    <childelement>child1</childelement>
   <parent>
 </element>
</elements>
is this valid? Its not working ..
thanks

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