query: #title: Check dates
  # Complex constraint from [[Property talk:P2568]]
  #
  SELECT ?item ?value ?publicationDate ?publicationDateBis {
  	?item wdt:P2568 ?value.
      ?item wdt:P577 ?publicationDate.
      ?value wdt:P577 ?publicationDateBis.
      FILTER (?publicationDate > ?publicationDateBis)  
  }