XSL: prevent duplicates in a hierarchy

Hi,

I have a hierarchy like this:

<hierarchy>
<class name="a">
<class name="b"/>
<class name="c"/>
</class>
<class name="d">
<class name="c"/>
<class name="e"/>
</class>
</hierarchy>

Now I want to go through the hierarchy and output each name, omitting duplicates (two nodes are equal if their names are equal). The desired output is:

a, b, c, d, e

and NOT:

a, b, c, d, c, e

How could I do that using XSLT? I'm not very familiar with XSLT. The approach I would take in, say, Java, is just to have some datastructure that remembers each name. However, I don't think that's possible in XSLT - or is it?

Cheers,
Knud

several solutions for that can be found here:

http://www.dpawson.co.uk/xsl/sect2/N2696.html

grtz