Give me a count of musicians who play an instrument developed by George Beauchamp?
SELECT DISTINCT COUNT(?uri) WHERE { ?x <http://dbpedia.org/property/keyPeople> <http://dbpedia.org/resource/George_Beauchamp> . ?uri <http://dbpedia.org/ontology/instrument> ?x  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/MusicalArtist>}
George_Beauchamp