query: #title: In the Museum without a link
  # Complex constraint from [[Property talk:P4683]]
  # Items that have [[Property:P195|collection&#32;<small dir="ltr">(P195)</small>]] -> [[d:Q214867|National Gallery of Art <small>(Q214867)</small>]], but that don't have a [[Property:P4683|National Gallery of Art artwork ID&#32;<small dir="ltr">(P4683)</small>]] link
  SELECT DISTINCT ?item ?url WHERE {
    ?item wdt:P195 wd:Q214867 .
    OPTIONAL { ?item wdt:P973 ?url } . 
    MINUS { ?item wdt:P4683 [] } .
  }  LIMIT 500