remove duplicates in each big entry

I don't find any example for my doubt about xsl, so i post my question.
Supose that i have the next xml:

<root>
<item>
<value>foo</value>
<value>foo</value>
<value>bar</value>
</item>
<item>
<value>foo</value>
<value>cat</value>
<value>cat</value>
</item>
</root>

<root>
<item>
<value>foo</value>
<value>bar</value>
</item>
<item>
<value>foo</value>
<value>cat</value>
</item>
</root>

Thanks,
psc