query: SELECT ?item ?sitelink ?wikipagina
    WITH {
     SELECT ?item ?itemLabel WHERE {
    ?item wdt:P6582 ?instrumentenmakerscode.
    }
  } AS %results
    WHERE {
    INCLUDE %results.
    OPTIONAL {
    ?sitelink schema:about ?item .
    ?sitelink schema:inLanguage ?lang .   
    ?sitelink schema:isPartOf [ wikibase:wikiGroup "wikipedia" ] .
    BIND(TRUE AS ?wikipagina)
    }
  }