question: Did M2 and M3 edit a film that M1 wrote and edited
query: SELECT count(*) WHERE {
  ?x0 a ns:film.film .
  ?x0 ns:film.film.edited_by M1 .
  ?x0 ns:film.film.written_by M1 .
  M2 ns:film.editor.film ?x0 .
  M3 ns:film.editor.film ?x0
  }