Did M3 star a film editor and star a star of M1 and M2
SELECT count(*) WHERE {
?x0 a ns:film.editor .
?x1 ns:film.actor.film/ns:film.performance.film M1 .
?x1 ns:film.actor.film/ns:film.performance.film M2 .
M3 ns:film.film.starring/ns:film.performance.actor ?x0 .
M3 ns:film.film.starring/ns:film.performance.actor ?x1
}