URGENT : Algorithm for exclusion elements

Hi people.
I have a problem with an algorithm that I don't know how to realize in XSLT.

I need to show in HTLM the <description> elements of all groups but only if
between an item/type="T" element and another item/type="T" element are
existing item/type="P" elements. In this way, only the SECOND GROUP
<description> elements should be processed. The problem is that I can know
that nobody <type>P</type> elements are present only after process the group
(between <type>T</type> elements) and it's too late.

Who can help me for this URGENT problem?

Thanks in advance.

<root>

 <!-- FIRST GROUP -->
 <item>
   <type>T</type>
   <description>title 1</description>
 </item>
 <item>
   <type>S</type>
   <description>summary 1</description>
 </item>

 <!-- SECOND GROUP -->
 <item>
   <type>T</type>
   <description>title 2</description>
 </item>
 <item>
   <type>P</type>
   <description>position 1</description>
 </item>
 <item>
   <type>S</type>
   <description>summary 3</description>
 </item>

 <!-- THIRD GROUP -->
 <item>
   <type>T</type>
   <description>title 3</description>
 </item>

</root>



 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list