What was a film producer that M1 and M2 were employed by and M3 and M4 were employed by
SELECT DISTINCT ?x0 WHERE {
?x0 a ns:film.producer .
?x0 ns:business.employer.employees/ns:business.employment_tenure.person M1 .
?x0 ns:business.employer.employees/ns:business.employment_tenure.person M2 .
?x0 ns:business.employer.employees/ns:business.employment_tenure.person M3 .
?x0 ns:business.employer.employees/ns:business.employment_tenure.person M4
}