removing duplicates problem

I am in the situation of wanting to create a node-set of all the 
    <person idref="Smith"/> and <author idref="Jones"/> tags with unique idref attributes. The tags can be found almost anywhere in the document.

I am making a list of <person> and <author> elements using:


<xsl:template name="people">
    <xsl:variable 
        name="all" 
        select=".//person[@idref]|.//author[@idref]" 
        />

then trying to remove duplicates by selecting into a new variable like this:

    <xsl:variable 
        name="unique" 
        select="$all[not(.=following::$all)]" 
        />

before looking them up from another document and passing them to a "person" template:

    <xsl:for-each select="$unique">
        <xsl:variable name="pid" select="(@idref)"/>
        <xsl:for-each select="document('../xml/data/people.xml')">
            <xsl:apply-templates select="id($pid)"/>
        </xsl:for-each>
    </xsl:for-each>
</xsl:template>


The line trying to remove the duplicates does not compile, I guess I'm trying this the wrong way ;-)

Any suggestions welcome.
I am using Saxon 5.1 btw, though I doubt the problem stems from there ;-)

regards Jeremy

   ___________________________________________________________________

   Jeremy Quinn                                           Karma Divers
                                                       webSpace Design
                                            HyperMedia Research Centre

   <mailto:jeremy@xxxxxxxxxxxxxxxxx>     <http://www.media.demon.co.uk>
    <phone:+44.[0].207.737.6831>        <pager:jermq@xxxxxxxxxxxxxxx>



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