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