checking for a node in the ancestor axis

Hi,

   I have a situation here, where I have to check for the node in the ancestor 
axis. I tried setting a flag depending upon _Ctrl node into a xsl:variable and 
checking 
for that variable later. But it doesn't seem like working. 

        <xsl:if test="$CtrlExists='1'"> in the following code is always turning 
out false

But I can't do <xsl:if test="../../_Ctrl">, b'cos my xml inside <Rpt_Inven> 
varies all the time.

I am sure there is a better way to do this. But I couldn't  get to it. Is there 
any proper way to do this.

Thanks a lot.

my xml:
<data xmlns="urn:abcd:layers">
        <Rpt_Inven xmlns="urn:abcd:RepInven">
                <Invens>
                        <Inven>
                                <Entity>Ent1</Entity>
                        </Inven>
                        <Inven>
                                <Entity>Ent2</Entity>
                        </Inven>
                        <Inven>
                                <Entity>Ent3</Entity>
                        </Inven>
                </Invens>
        </Rpt_Inven>
        <!-- This node is optional. Doesn't exists all the time -->
        <_Ctrl xmlns="" xmlns:lay="urn:abcd:layers"  
xmlns:rep="urn:abcd:RepInven" xmlns:obj="urn:abcd:objects">
                <_Table>
                        <_Col name="Entity"/>
                </_Table>
        </_Ctrl>
</data>

my xsl:

<xsl:stylesheet version="1.0" xmlns="" xmlns:lay="urn:abcd:layers" 
xmlns:rep="urn:abcd:RepInven" xmlns:xsl="http://www.w3.org/1999/XSL/Transform";>
        <xsl:output method="xml" encoding="UTF-8"/>
        <xsl:template match="lay:data">
                <xsl:variable name="CtrlExists">
                        <xsl:choose>
                                <xsl:when test="_Ctrl">
                                        <xsl:value-of select="'1'"/>
                                </xsl:when>
                                <xsl:otherwise>
                                        <xsl:value-of select="'0'"/>
                                </xsl:otherwise>
                        </xsl:choose>
                </xsl:variable>
                <_Ctrl>
                        <xsl:for-each select="rep:Rpt_Inven/rep:Invens">
                                <_Table>
                                        <_Col name="Entity">
                                                <xsl:if test="$CtrlExists='1'">
                                                        <xsl:for-each 
select="rep:Inven/rep:Entity">
                                                                <xsl:sort 
select="."/>
                                                                <_Item>
                                                                        
<xsl:value-of select="."/>
                                                                </_Item>
                                                        </xsl:for-each>
                                                </xsl:if>
                                        </_Col>
                                </_Table>
                        </xsl:for-each>
                </_Ctrl>
        </xsl:template>
</xsl:stylesheet>




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