Your input wasn't well formed but after fixing that, i think this does
what you want. Th e"uniqueness" aspect is automatic given xpath1's node
set semantics as sets never have repeated values.


<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  
<xsl:key name="c" match="country" use="@id"/>
<xsl:key name="cg" match="countryGroup" use="@groupID"/>

 <xsl:template match="data">
   <xsl:apply-templates select="businesses/business"/>
 </xsl:template>

 <xsl:template match="business">
   <xsl:text>&#10;</xsl:text>
   <xsl:value-of select="name"/>
   <xsl:text>: </xsl:text>
   <xsl:for-each select="key('c',key('cg',countryGroup/@included)/country/@included)">
     <xsl:value-of select="."/>
     <xsl:text> </xsl:text>
   </xsl:for-each>
 </xsl:template>

</xsl:stylesheet>

$ saxon gm.xml gm.xsl
<?xml version="1.0" encoding="utf-8"?>
Acme: United States Mexico 
Another Acme: Canada Mexico 


David

oops I just use saxon on the command line, silly me:-)