@incollection{MichelsBorchert2009,
  author    = {Michels, A. and Borchert, J{\"o}rg},
  title     = {Beschaffungsstrategien an der Schnittstelle Energiehandel/Vertrieb},
  series = {Energiehandel in Europa},
  booktitle = {Energiehandel in Europa},
  editor    = {Zenke, Ines},
  edition   = {2. Aufl.},
  publisher = {Beck},
  address   = {M{\"u}nchen},
  isbn      = {978-3-406-58373-5},
  pages     = {467 -- 481},
  year      = {2009},
  language  = {de}
}
@incollection{BorchertMichels2012,
  author    = {Borchert, J{\"o}rg and Michels, A.},
  title     = {Beschaffungsstrategien an der Schnittstelle Energiehandel / Vertrieb},
  series = {Energiehandel in Europa},
  booktitle = {Energiehandel in Europa},
  editor    = {Zenke, ines},
  edition   = {3. Aufl.},
  publisher = {Beck},
  address   = {M{\"u}nchen},
  isbn      = {978-3-406-63237-2},
  pages     = {508 -- 522},
  year      = {2012},
  language  = {de}
}