duplicate removal

Given some r elements which contains duplicates <cat-num>
but different <bibno> children, I'm trying to using keys to resolve.

  <xsl:key name="multiBooks" match="r" use="cat-num"/>
  <xsl:template match="doc">
    <xsl:apply-templates   select="r [cat-num and 
                                   generate-id(.) =
generate-id(key('multiBooks',cat-num))]"/>
  </xsl:template>


This finds all the duplicate cat-num entries.
The processing model doesn't however, allow
me to identify if the first one has different
bibno child to the others, which is what I need.

Any suggestions for an alternative to the 
apply-templates above, which would allow
me to check if each one had the same bibno child
as the first?

TIA DaveP.

xml below.


<doc>
  </r><r id="d0e218251">
      <bibno>056543</bibno>
      <cat-num>546</cat-num>
           <m100>
         <surname>Ridgway</surname>
         <f-name>John</f-name>
      </m100>
      <m245>
         <ttl>A fighting chance</ttl>
         <au>(by Captain John Ridgway and Sargeant Chay Blyth)</au>
      </m245>
      <m655/>
      <m700>
         <surname>Blyth</surname>
         <f-name>Chay</f-name>
      </m700>
</r>
 <!-- Duplicate, i.e. same tb number, different bib number -->
 <!-- Implies that this tb has two books on it. -->
 <r id="d0e218251">
      <bibno>12345</bibno>
      <cat-num>546</cat-num>
      <m100>
         <surname>Ridgway</surname>
         <f-name>John</f-name>
      </m100>
      <m245>
         <ttl>A fighting chance</ttl>
         <au>(by Captain John Ridgway and Sargeant Chay Blyth)</au>
      </m245>
     <m700>
         <surname>Blyth</surname>
         <f-name>Chay</f-name>
      </m700>
 </r>
</doc>

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