question: Was M3 a prequel of a film whose executive producer executive produced M2 and wrote M1
query: SELECT count(*) WHERE {
  ?x0 a ns:film.film .
  ?x0 ns:film.film.executive_produced_by ?x1 .
  ?x1 ns:film.producer.films_executive_produced M2 .
  ?x1 ns:film.writer.film M1 .
  M3 ns:film.film.sequel ?x0
  }