FUNCTION grandchildren($p)
{
   RETURN $p/person/person
        | $p/@spouse->/person/person
        | $p/person/@spouse-/person
        | $p/@spouse->/person/@spouse->/person
}

<result>
   (
   FOR $gp IN document("census.xml")//person
   LET $gc := grandchildren($gp)
   WHERE exists($gc)
   RETURN
      <grandparent name = $gp/name>
         (
         FOR $x IN $gc
         RETURN <grandchild name = $x/name ></grandchild>
         )
      </grandparent>
   )
</result>