List the producer of the TV shows whose company is HBO.
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/ontology/company> <http://dbpedia.org/resource/HBO> . ?x <http://dbpedia.org/ontology/producer> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/TelevisionShow>}
HBO