@Book{Biethahn.2004b,
  author = {Biethahn, Jörg and Mucksch, Harry and Ruf, Walter},
  title  = {Grundlagen},

  year   = {2004},
  number = {},
  url    = {},

  const  = {\ text}
}
@Book{Biethahn.1997,
  author = {Biethahn, Jörg and Mucksch, Harry and Ruf, Walter and Almstedt, Matthias and Aschenbach, Frank and de Edda Boer},
  title  = {Entwicklungsmanagement},

  year   = {1997},
  number = {},
  url    = {},

  const  = {\ text}
}