Muenchian keys ... plus a bit?

Given

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE idx [
<!ELEMENT idx (ent+)>
<!ELEMENT ent (item, pge+)>
<!ELEMENT item (#PCDATA)>
<!ELEMENT pge  (#PCDATA)>
<!ATTLIST pge key (t|f) 'f'>


]>

<idx>
 <ent>
  <item>content</item>
  <pge key="f">98</pge>
 </ent>
 <ent>
  <item>content</item>
  <pge key="f">108</pge>
  <pge>110</pge>
 </ent>
 <ent>
  <item>another</item>
  <pge key="f">100</pge>
 </ent>
 <ent>
  <item>zero</item>
  <pge key="t">210</pge>
 </ent>
</idx>


And indexing DTD.

I want to present it as

A  B  C .... Z
(each hotlinked to the start of that letter).

Then 

A  (the anchor)

aardvark, page 1,67,79
  (say with page 67
-------------------
B 

bathtub, page 3,5,7

------------------

Z

zero, page 210
   (210 in bold, its the main entry)
etc.

Two pass solution, first sorting, to make data entry easy.
Being lazy, I don't always remember that I've already made
an entry for a particular element, so there are duplicates.
the <item> is duplicated, but the page numbers are not,
hence the 'remove duplicates' approach of keys only partially works.
Hence the Muenchian plus (I think :-).

Question, how to remove the duplicate entries without losing
the page numbers associated with the duplicate?

I found this quite an interesting stylesheet, till I couldn't
figure out the key definitions/usage, then I was stopped.

I have everything except the 'remove duplicates' bit.

Any help appreciated.

Regards daveP
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