Sorting with variable

Hello everybody

<xsl:for-each select="//day">
        <xsl:variable name="day" select="."/>
                <xsl:for-each 
select="//gv/activity[generate-id()=generate-id(key('activity_key',@name))]">
                        <xsl:sort select="./hits" data-type="number" 
order="descending"/>       
                        <xsl:variable name="uname" select="@name"/>
                        <xsl:variable name="activity" 
select="$day/gv/activity[(_at_)name=$uname]/@name"/>
                        <xsl:variable name="summe" 
select="sum($activity/../..//activity[(_at_)name=$uname]/hits)"/>            
                        <!-- $summe has the right value -->
                        <xsl:sort select="$summe" data-type="number" 
order="descending"/>       
                        <!-- print unsorted -->
                        <xsl:value-of select="$summe"/>
                </xsl:for-each>
</xsl:for-each>

My goal is, to sort the "activity" with the "summe". So i want to have for 
example the following result:

act1                       34
act2                       12
act3                         1

But the script doesnt work. Maybe because i use a variable in the 
sort-statement?

Anyone knows something about this?

Kindly regards
Florian Mueller

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