xsl:if question

I want to show a block of text only if two xml element are different.  I'm
not sure what the error is in the following;  Please if someone could
explain why it doesn't work, I would greatly appreciate it.

...
<xsl:template match="/foo">

    <xsl:if test="{/foo/bar} != {/foo/cow}">    la la la ..... </xsl:if>

<!-- The above line is where my confusion lies.  I want to test to see if
the two element
are not the same.  It always evaluates to false, which is not the desired
behavior -->


</xsl:template>
...

-matt


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