Checking for instance of xs:integer

Hi,

    I have the following code :

<?xml version="1.0"?>
<xsl:stylesheet version="2.0"
        xmlns:xs="http://www.w3.org/2001/XMLSchema"
        xmlns:xdt="http://www.w3.org/2003/11/xpath-datatypes"
        xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

        <xsl:output omit-xml-declaration="yes" />

        <xsl:template match="/">
                <xsl:variable name="var">
                        <xsl:element name="a">
                                <xsl:value-of select="xs:integer(2)
treat as xs:integer" />
                        </xsl:element>
                </xsl:variable>

                <xsl:choose>
                        <xsl:when test="$var/a instance of xs:integer">
                                yes
                        </xsl:when>
                        <xsl:otherwise>
                                no
                        </xsl:otherwise>
                </xsl:choose>
        </xsl:template>

</xsl:stylesheet>

...where I'm trying to detect if a variable has an integer value. The
output that I currently get is :

bash-2.05b$ java net.sf.saxon.Transform intck.xsl intck.xsl 

                                no

    At first I thought that this is because the xsl:value-of that is
used to assign the value of $var/a was producing either a string or an
untypedAtomic value. However, changing the "xsl:when" to test for
xs:string and xsd:untypedAtomic didnt work either. Is there any way to
get this to work without using a schema aware processor?

Thanks,
Kenneth