Comparing two variables

I've been looking the archives but didn't found any thread about it.
I've also checked Dave's FAQ.

I'm writing a stylesheet to generate presentations in HTML.
I've wrote two named templates called "find.nextslide" and
"find.lastslide" to generate a link to
those slides (that appears on top left of present slide).

My problem is who can I compare the $next variable, which
is the position of actual "<slide>" element plus 1, and
$last variable. If $next > $last so $result = $last else
$result = $next.

I was not really sure if $next and $last were number value or
string, so I tried:

test="number($next) > number($last)"
test="$next > number($last)"

My XSLT processor, xsltproc (v. 1.1.3), complains:
xmlXPathCompOpEval: parameter error
runtime error: file xpresent-common.xsl line 98 element value-of
xsltValueOf: text copy failed

line 98 is:
<xsl:value-of select="concat('slide',$result,'.html')"/>
of "find.nextslide" named template.

Am I messing things up? I really can't figure out...
Any ideas?

<!-- returns the last slide number -->
  <xsl:template name="find.lastslide">
    <xsl:value-of select="count(/xpresent/slide)"/>
  </xsl:template>

<!-- creates an "slideX.html" string -->
<xsl:template name="find.nextslide">
    <xsl:variable name="next" select="position() + 1"/>
    <xsl:variable name="last"><xsl:call-template
	name="find.lastslide"/></xsl:variable>
    <xsl:choose>
      <xsl:when test="$next &gt; $last">
	<xsl:variable name="result"><xsl:value-of select="$last"/></xsl:variable>
      </xsl:when>
      <xsl:otherwise>
	<xsl:variable name="result"><xsl:value-of
	    select="$next"/></xsl:variable>
      </xsl:otherwise>
    </xsl:choose>
    <xsl:value-of select="concat('slide',$result,'.html')"/>
  </xsl:template>

[]'s
Lucas Brasilino
brasilino@xxxxxxxxxxxxxxxx
http://www.recife.pe.gov.br
Emprel -	Empresa Municipal de Informatica (pt_BR)
		Municipal Computing Enterprise (en_US)
Recife - Pernambuco - Brasil
Fone: +55-81-34167078