How many {killed by} are to/by {Perseus} ?
Perseus killed how many?
SELECT (COUNT(?sub) AS ?value ) { ?sub wdt:P157 wd:Q130832 }
SELECT (COUNT(?sub) AS ?subs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> ?sub .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P157> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> http://wikidata.dbpedia.org/resource/Q130832 .
} 

What number were killed by Perseus?