question: Which art director of M1 was a American art director of M2
query: SELECT DISTINCT ?x0 WHERE {
  ?x0 ns:film.film_art_director.films_art_directed M1 .
  ?x0 ns:film.film_art_director.films_art_directed M2 .
  ?x0 ns:people.person.nationality ns:m.09c7w0
  }