query: SELECT ?item ?itemLabel ?subject ?subjectLabel ?article WHERE {
  
    ?item wdt:P1433 wd:Q15987216 .
    ?item wdt:P31 wd:Q19389637.
    ?item wdt:P921 ?subject .
    ?article 	schema:about ?subject ;
  			schema:isPartOf <https://en.wikisource.org/> .
  
    OPTIONAL { ?article2 schema:about ?subject ; schema:isPartOf <https://en.wikipedia.org/> }
    FILTER ( !bound(?article2) )
    
      SERVICE wikibase:label {
          bd:serviceParam wikibase:language "en" .
      }
  
  } 