<publisher_list>
     {for $p in distinct-values(document("bib.xml")//publisher)
      return
          <publisher>
              <name> {$p/text()} </name> 
              {for $b in document("bib.xml")//book[publisher = $p]
                  return
                     <book>
                        {$b/title}
                        {$b/price}
                     </book> 
                  sortby(price descending)
              }
          </publisher> 
      sortby(name)
     }
</publisher_list>