@Electronic{schumann2011grundzge,
  author = {Schumann, Jochen and Ströbele, Wolfgang and Meyer, Ulrich},
  title  = {Grundzüge der mikroökonomischen Theorie},

  year   = {2011},
  number = {},
  url    = {http://dx.doi.org/10.1007/978-3-642-21225-3},

  const  = {\ text}
}