How many {performer} are to/by {Boris Grebenshchikov} ?
Who is the performer Boris Grebenshcikov?
SELECT (COUNT(?sub) AS ?value ) { ?sub wdt:P175 wd:Q542101 }
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/P175> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> http://wikidata.dbpedia.org/resource/Q542101 .
} 

Who is Boris Grebenshcikov?