Who is the author with the largest number of papers about semantic representation in music research problem? 
SELECT ?author
WHERE {
  ?papers rdf:type orkgc:Paper.
  ?papers orkgp:P31 ?contrib.
  ?contrib orkgp:P32 ?research_problems.
  ?research_problems rdfs:label ?research_problems_labels.
  FILTER(REGEX(?research_problems_labels, "semantic representation in music", "i"))
  ?papers orkgp:P27 ?authors.
  OPTIONAL {
    ?authors rdfs:label ?authors_labels
  }
  BIND(IF(BOUND(?authors_labels), ?authors_labels, ?authors) AS ?author)
}
ORDER BY DESC(COUNT(?author))
LIMIT 1