ASK WHERE {
 <http://www.w3.org/2006/07/SWD/RDFa/testsuite/xhtml1-testcases/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) )
}