Did M2 and M3 star a art director that directed M1
SELECT count(*) WHERE {
?x0 a ns:film.film_art_director .
?x0 ns:film.director.film M1 .
M2 ns:film.film.starring/ns:film.performance.actor ?x0 .
M3 ns:film.film.starring/ns:film.performance.actor ?x0
}