Need to output an opening or closing tag by itself

I have a simple XSLT problem for the gurus.


This is my input document:
<root>
  <e t="a"/>
  <f/>
  <f/>
  <e t="b"/>
</root>


This is the output document I want to produce:
<root>
  <e>
    <f/>
    <f/>
  </e>
</root>


This is the stylesheet I wrote to do the transformation:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet
  version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:template match="/root">
    <root>
      <xsl:apply-templates/>
    </root>
  </xsl:template>

  <xsl:template match="e">
    <xsl:choose>
      <xsl:when test="@t ='a'">
        <e>
      </xsl:when>
      <xsl:when test="@t ='b'">
        </e>
      </xsl:when>
      <xsl:otherwise>
        <xsl:message terminate="yes">
          Unexpected data in attribute t.
        </xsl:message>
      </xsl:otherwise>
    </xsl:choose>
  </xsl:template>

  <xsl:template match="f">
    <xsl:copy/>
  </xsl:template>
</xsl:stylesheet>


Here is the Saxon output:
$ java -jar "c:\Program Files\Saxon\saxon9.jar" -o out.xml in.xml
test.xslt
Error on line 16 column 9 of
file:/C:/Documents%20and%20Settings/DFREY/Desktop/test/test.xslt:
  SXXP0003: Error reported by XML parser: The element type "e" must be
terminated by the
  matching end-tag "</e>".
Failed to compile stylesheet. 1 error detected.


I understand that the source of the error is that the XSLT file is not
valid XML because the <e> tag doesn't have a matching </e> tag in the
right place.

How can I work around this issue to solve my problem?

Thanks,
David