@unpublished{Bergmann1999,
  author  = {Ralph Bergmann},
  title   = {Plan Abstraction with Change of Representation Language},
  institution = {Fachbereich Informatik},
  year    = {1999},
  url  = {http://nbn-resolving.de/urn:nbn:de:hbz:386-kluedo-1703},
}