query: #title: Use follows and followed by consistently
  # Complex constraint from [[Property talk:P179]]
  # Use of P155 or P156 pointing to an item that does not use the opposite qualifier pointing back
  SELECT ?item WHERE {
    ?item p:P179 ?statement .
    {
      ?statement ps:P179 ?a; pq:P155 ?y .
      FILTER NOT EXISTS {
        ?y p:P179 [ ps:P179 ?a; pq:P156 ?item ].
      }
    } UNION {
      ?statement ps:P179 ?a; pq:P156 ?y .
      FILTER NOT EXISTS {
        ?y p:P179 [ ps:P179 ?a; pq:P155 ?item ].
      }
    }
  }