Were M4 and M5 written by a person that M1 , M2 , and M3 employed
SELECT count(*) WHERE {
?x0 a ns:people.person .
?x0 ns:people.person.employment_history/ns:business.employment_tenure.company 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 .
M4 ns:film.film.written_by ?x0 .
M5 ns:film.film.written_by ?x0
}