ASK WHERE {
 <http://www3.aptest.com/standards/rdfa-html/testsuite/0111.html> <http://www.w3.org/1999/xhtml/vocab#next> ?a .
 ?a <http://www.w3.org/1999/xhtml/vocab#next> ?b .
  FILTER (ISBLANK(?a) && ISBLANK(?b) )
}