What are the research problems of the cultural history field?
SELECT DISTINCT ?research_problems, ?research_problems_labels
WHERE {
  ?papers rdf:type orkgc:Paper.
  ?papers orkgp:P30 ?research_fields.
  ?research_fields rdfs:label ?research_fields_labels. 
  FILTER(REGEX(?research_fields_labels, "cultural history", "i"))
  ?papers orkgp:P31 ?contrib.
  ?contrib orkgp:P32 ?research_problems.
  ?research_problems rdfs:label ?research_problems_labels.
}