Was a art director that M2 and M3 employed M1 's writer
SELECT count(*) WHERE {
?x0 a ns:film.film_art_director .
?x0 ns:film.writer.film M1 .
?x0 ns:people.person.employment_history/ns:business.employment_tenure.company M2 .
?x0 ns:people.person.employment_history/ns:business.employment_tenure.company M3
}