machine_question: who did darth vaders voice and who also wrote Voices and silences
question: Who wrote Voices and silences and also did Darth Vader's voice?
sparql: PREFIX ns: <http://rdf.freebase.com/ns/>
  SELECT DISTINCT ?x
  WHERE {
  FILTER (?x != ns:m.0f2y0)
  FILTER (!isLiteral(?x) OR lang(?x) = '' OR langMatches(lang(?x), 'en'))
  ns:m.0f2y0 ns:film.film_character.portrayed_in_films ?y .
  ?y ns:film.performance.actor ?x .
  ?y ns:film.performance.special_performance_type ns:m.02nsjvf .
  ?x ns:book.author.works_written ns:m.067z76z . 
  }
webqsp_question: who did darth vaders voice