SELECT ?who ?g ?mbox FROM <http://example.org/dft.ttl> FROM NAMED <http://example.org/alice> FROM NAMED <http://example.org/bob> WHERE {
  ?g <http://purl.org/dc/elements/1.1/publisher> ?who .
  GRAPH ?g {
    ?x <http://xmlns.com/foaf/0.1/mbox> ?mbox .
  }
}