[xsl] Are these equivalent XPath expressions for determining that there are no duplicates in a list of items?

["Costello, Roger L." <costello@xxxxxxxxx>]

Hi Folks,

Are there no duplicate websites in this list:

    <Websites>
        <Website id="Amazon"> http://www.amazon.com </Website>
        <Website id="Apple"> http://www.apple.com </Website>
        <Website id="Ebay"> http://www.ebay.com </Website>
        <Website id="Google"> http://www.google.com </Website>
        <Website id="Microsoft"> http://www.microsoft.com </Website>
        <Website id="VirginAtlantic"> http://www.virgin-atlantic.com
</Website>
    </Websites>

Here is an XPath 2.0 expression to answer that question (thanks to Dimitre):

    empty(Websites/*[index-of(../*,.)[2]])

Here is an XPath 1.0 expression to answer that question:

    not(//Websites/*[. = preceding-sibling::*])

Are there any situations where those two XPath expressions differ in their
answer?

/Roger