select distinct p.firstname, p.lastname from person p where
	(select count(*) from filmparticipation fp, filmitem f where
	p.personid = fp.personid and f.filmid = fp.filmid
 	and fp.parttype = 'cast' and f.filmtype = 'C') > 50
and not exists
	(select * from person p2, filmparticipation fp, filmparticipation fp2, filmitem f where
	f.filmid = fp.filmid and f.filmid = fp2.filmid
	and p.personid = fp.personid and p2.personid = fp2.personid and p2.lastname > p.lastname);