muenchian grouping is your friend.

add

<xsl:key name="page" match="*[@page-num]" use="@page-num"/>

then to test if the current node is the first node with a given page-num
you just need

<xsl:if test="generate-id(.)=generate-id(key('page',@page-num)[1])">
 ...

as the key will return all the nodes with the current page-num, and the
generate-id test tests that the current node is the first of those in
document order.

To comment on your posted code

<xsl:template match="/">
<xsl:for-each select="@page-num">

/ is the document root so has no attributes so this is iterating over
the empty node set and will therefore do nothing.

You could change it to <xsl:for-each select="//*@page-num"> but the
above key is likely to be a lot more efficient than building a list of
unique pages before starting.

David

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