query: SELECT DISTINCT ?authorstring
  WHERE {
    hint:Query hint:optimizer "None".
  {  SERVICE wikibase:mwapi {
      bd:serviceParam wikibase:api "Search";
                      wikibase:endpoint "www.wikidata.org";
                      mwapi:srsearch "wang zhang haswbstatement:P31=Q13442814".
      ?page_title wikibase:apiOutput mwapi:title.
    }}
    
    BIND(IRI(CONCAT(STR(wd:), ?page_title)) AS ?item)
  #  FILTER NOT EXISTS { ?item wdt:P921 wd:Q27318. }
    
    ?item wdt:P31 wd:Q13442814;
          wdt:P2093 ?authorstring.
  #  FILTER CONTAINS(LCASE(?authorstring), "zhang").
    FILTER(REGEX(LCASE(?authorstring), ".*(wang).*(zhang).*"))
  }
  LIMIT 50
  
  