query: #title: Elo ratings without proper source
  # Complex constraint from [[Property talk:P1087]]
  # Elo ratings that do not have either a link to ratings.fide.com or olimpbase.org. Particularly, "imported from" is not a proper source.
  SELECT ?item ?elo WHERE {
    ?item p:P1087 ?s .
    FILTER NOT EXISTS { ?s prov:wasDerivedFrom/(pr:P248|pr:P854) ?refHandle }
    ?s ps:P1087 ?elo .
  }