query: #title: should have P31=category
  # Complex constraint from [[Property talk:P31]]
  # TODO: add P31
  SELECT ?item ?n
  {
    hint:Query hint:optimizer "None".
    ?item wikibase:statements 0 . 
    [] schema:about ?item ; schema:name ?n ; schema:isPartOf ?part . 
    ?part wikibase:wikiGroup "wikipedia". 
    FILTER( strstarts(?n , "Category:") ) 
  }  
  LIMIT 100