(Q10) List each publisher and the average price of its books.

FOR $p IN distinct(document("bib.xml")//publisher)
LET $a := avg(document("bib.xml")
   /book[publisher = $p]/price)
RETURN 
   <publisher>
      <name> $p/text() </name> ,
      <avgprice> $a </avgprice>
   </publisher>

XSLT equivalent to (Q10)

<xsl:transform version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:template match="/">
    <xsl:for-each select="document('bib.xml')//publisher[not(.=preceding::publisher)]">
      <xsl:variable name="prices" 
                    select="document('bib.xml')/book[publisher=current()]/price"/>
      <xsl:variable name="avgPrice" select="sum($prices) div count($prices)"/>
      <publisher>
        <name><xsl:value-of select="."/></name>
        <avgprice><xsl:value-of select="$avgPrice"/></avgprice>
      </publisher>
    </xsl:for-each>
  </xsl:template>
</xsl:transform>