query: #title: Unique value
  # Complex constraint from [[Property talk:P374]]
  # A value must not be used by multiple entities at the same point in time
  SELECT DISTINCT ?item1 ?item2 ?value
    WHERE {
      ?item1 wdt:P374 ?value .
      ?item2 wdt:P374 ?value .
      FILTER( ?item1 != ?item2 && STR(?item1) < STR(?item2) ) .
      MINUS {
        ?item1 p:P374 ?st1 . ?st1 ps:P374 ?value; pq:P582 ?end .
        ?item2 p:P374 ?st2 . ?st2 ps:P374 ?value; pq:P580 ?start .
        FILTER( ?end < ?start )
      }
      MINUS {
        ?item1 p:P374 ?st1 . ?st1 ps:P374 ?value; pq:P580 ?start .
        ?item2 p:P374 ?st2 . ?st2 ps:P374 ?value; pq:P582 ?end .
        FILTER( ?end < ?start )
      }
    }