Were M1 and M2 written by and edited by a film editor
SELECT count(*) WHERE {
?x0 a ns:film.editor .
M1 ns:film.film.edited_by ?x0 .
M1 ns:film.film.written_by ?x0 .
M2 ns:film.film.edited_by ?x0 .
M2 ns:film.film.written_by ?x0
}