query: #title: Office holders shouldn't end before starting
  # Complex constraint from [[Property talk:P39]]
  # start date should be < end date. If two terms are mixed, separate statements should be made
  SELECT ?item ?position ?start ?end WHERE {
    ?statement pqv:P580 ?start_node; pqv:P582 ?end_node . 
    ?start_node wikibase:timePrecision 11; wikibase:timeValue ?start . 
    ?end_node wikibase:timePrecision 11; wikibase:timeValue ?end . FILTER( ?end < ?start ) . 
    ?item p:P39 ?statement .
    ?statement ps:P39 ?position .
    ?item wdt:P31 wd:Q5 
  }