ASK WHERE {
 <http://rdfa.info/test-suite/test-cases/rdfa1.1/html5/0111.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) )
}