How many publisher have been founded by american citizens?
SELECT DISTINCT COUNT(?uri) WHERE { ?x <http://dbpedia.org/ontology/stateOfOrigin> <http://dbpedia.org/resource/United_States> . ?uri <http://dbpedia.org/ontology/founder> ?x  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Publisher>}
United_States