@incollection{Stahlknecht1991,
  author    = {Stahlknecht, P},
  title     = {Arbeitsbuch Wirtschaftsinformatik},
  address   = {Berlin, Heidelberg, New York},
  year      = {1991},
  language  = {mul}
}
@article{BalzKuehl1991,
  author    = {Balz, Ulrich and K{\"u}hl, Carsten},
  title     = {Grundz{\"u}ge der Marktwirtschaft},
  series = {Schriftreihen des Instituts f{\"u}r Finanzwissenschaft},
  journal   = {Schriftreihen des Instituts f{\"u}r Finanzwissenschaft},
  year      = {1991},
  language  = {de}
}