ASK WHERE {
 <http://rdfa.digitalbazaar.com/test-suite/test-cases/xhtml1/0111.xhtml> <http://www.w3.org/1999/xhtml/vocab#next> ?a .
 ?a <http://www.w3.org/1999/xhtml/vocab#next> ?b .
  FILTER (ISBLANK(?a) && ISBLANK(?b) )
}