@article{Petersen2002,
  author    = {Petersen, Hans-Georg},
  title     = {Die Einfachsteuer des "Heidelberger Steuerkreises"},
  year      = {2002},
  language  = {de}
}
@article{Petersen2002,
  author    = {Petersen, Hans-Georg},
  title     = {Die Einfachsteuer im empirischen Test},
  isbn      = {3-8005- 2060-5},
  year      = {2002},
  language  = {de}
}