using a node set in a xsl:variable in an xsl:key

I have this code in my xsl:

                                         <xsl:variable name="a">
                                             <division>
                                                <fullname>
                                                 <name>a</name>
                                                 </fullname>
                                                 <fullname>
                                                 <name>b</name>
                                                 </fullname>
                                                 <fullname>
                                                 <name>c</name>
                                                 </fullname>
                                                <fullname>
                                                 <name>a</name>
                                                 </fullname>
                                             </division>
                                         </xsl:variable>

....
                                         <xsl:for-each 
select="$a/division/fullname">
                                            <xsl:value-of select="name" />
                                         </xsl:for-each>
Which produces this result:   abca

what I would like to do is use an xsl:key, and the Meunchin method in order to 
get:  abc
as my result (removing duplicates).  Anyone have any thoughts on this?



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