What film producer wrote a film 's sequel and prequel
SELECT DISTINCT ?x0 WHERE {
?x0 a ns:film.producer .
?x0 ns:film.writer.film ?x1 .
?x1 ns:film.film.prequel ?x2 .
?x1 ns:film.film.sequel ?x2 .
?x2 a ns:film.film
}