Did M3 employ a art director that M1 and M2 employed
SELECT count(*) WHERE {
?x0 a ns:film.film_art_director .
?x0 ns:people.person.employment_history/ns:business.employment_tenure.company M1 .
?x0 ns:people.person.employment_history/ns:business.employment_tenure.company M2 .
M3 ns:business.employer.employees/ns:business.employment_tenure.person ?x0
}