Dimitre's solution is brilliant..

Here is a solution using the node-set extension function:

Sorry, I didn't state it explicitly, I need xslt 1.0 for browsers (no
extensions),
but thanks anyway.

> xslt 1.0 - I've a set of nodes, for which I want
> a. to replace some values (most will not change), then
> b. eliminate the duplicates and sort them.
..............................................................................
> The text nodes represent URI's and are then used to
> create html links. So far I was only able to write in
> 2 different task what should be done in one:
>

One simple way to do this:

The following transformation:

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:output omit-xml-declaration="yes" indent="yes"/>

 <xsl:key name="kb" match="b[not(. = ../../e2/f/@c)]"  use="."/>
 <xsl:key name="kb" match="@b1" use="../../../e1/b[. = current()/../@c]"/>
  <xsl:key name="kDist" match="b | @b1" use="."/>

        <xsl:template match="/">
          <e3>
            <xsl:for-each select="key('kb', */e1/b)[generate-id() =
                                generate-id(key('kDist', .)[1])]">
              <xsl:sort/>

        <b2><xsl:value-of select="."/></b2>
      </xsl:for-each>
          </e3>
        </xsl:template>
</xsl:stylesheet>

when applied on the provided source xml document:

<a>
        <e1>
                <b>abc</b>
                <b>abd</b>
                <b>abe</b>
                <b>abf</b>
                <b>abg</b>
                <b>abh</b>
                <b>abd</b>
        </e1>
        <e2>
                <f c="abe" b1="abc"/>
                <f c="abf" b1="abj"/>
                <f c="abg" b1="abi"/>
                <f c="abh" b1="abi"/>
        </e2>
</a>

produces the wanted result:

<e3>
        <b2>abc</b2>
        <b2>abd</b2>
        <b2>abi</b2>
        <b2>abj</b2>
</e3>

I'm still fascinated by Dimitre's solution. I also tried a first modification
(but without success): <e1> represents a response from a web service,
but <e2> is supplied by me and fairly static. So it would make sense to
put it in a separate document (teste2.xml), to enable the browser to cache it.
       <e2>
               <f c="abe" b1="abc"/>
               <f c="abf" b1="abj"/>
               <f c="abg" b1="abi"/>
               <f c="abh" b1="abi"/>
       </e2>
The first key definition
  <xsl:key name="kb" match="b[not(. = ../../e2/f/@c)]"  use="."/>
I assume should become
  <xsl:key name="kb" match="b[not(.
=document('teste2.xml')/e2/f/@c)]"  use="."/>
but I have no idea how to change the second
  <xsl:key name="kb" match="@b1" use="../../../e1/b[. = current()/../@c]"/>
How can I get a xpath expression for the (primary) source document if the
context is in another source document?
Regards, Manfred