query: #title: Person dies before spouse is born
  # Complex constraint from [[Property talk:P26]]
  #
  SELECT ?item ?spouse WHERE { 
    ?item wdt:P26 ?spouse . 
    ?item p:P570/psv:P570/wikibase:timeValue ?death . 
    ?spouse p:P569/psv:P569/wikibase:timeValue ?birth_of_spouse . 
    FILTER (?death < ?birth_of_spouse)
  }