Was M2 edited by a film editor that edited M1 and edited by M3 and M4
SELECT count(*) WHERE {
?x0 a ns:film.editor .
?x0 ns:film.editor.film M1 .
M2 ns:film.film.edited_by ?x0 .
M2 ns:film.film.edited_by M3 .
M2 ns:film.film.edited_by M4
}