What did a person executive produce and a writer of M1 and M2 executive produce
SELECT DISTINCT ?x0 WHERE {
?x0 ns:film.film.executive_produced_by ?x1 .
?x0 ns:film.film.executive_produced_by ?x2 .
?x1 a ns:people.person .
?x2 ns:film.writer.film M1 .
?x2 ns:film.writer.film M2
}