@book{PfeifferKnepper1998,
  author    = {Pfeiffer, Johann and Knepper, Ludger},
  title     = {Diplom Ingenieur/Diplom Ingenieurin (Fachhochschule) Maschinenbau Konstruktionstechnik},
  publisher = {Bertelsmann},
  address   = {Bielefeld},
  pages     = {Losebl.-Ausg.},
  year      = {1998},
  language  = {de}
}
@book{PfeifferKnepper1999,
  author    = {Pfeiffer, Johann and Knepper, Ludger},
  title     = {Diplom-Ingenieur/Diplom-Ingenieurin (Fachhochschule) Maschinenbau Energie- und W{\"a}rmetechnik},
  publisher = {Bertelsmann},
  address   = {Bielefeld},
  pages     = {Losebl.-Ausg.},
  year      = {1999},
  language  = {de}
}