question: Which film was written by M1 , M2 , and M3 and was written by a screenwriter
query: SELECT DISTINCT ?x0 WHERE {
  ?x0 a ns:film.film .
  ?x0 ns:film.film.written_by ?x1 .
  ?x0 ns:film.film.written_by M1 .
  ?x0 ns:film.film.written_by M2 .
  ?x0 ns:film.film.written_by M3 .
  ?x1 a ns:film.writer
  }