@Book{imhof1997kassel,
  author = {Imhof, Michael},
  title  = {Kassel : Stadtführer},

  year   = {1997},
  number = {},
  url    = {http://www.amazon.de/Kassel-Stadtf%C3%BChrer-Michael-Imhof/dp/3932526074/ref=sr_1_1?s=books&ie=UTF8&qid=1435743690&sr=1-1&keywords=kassel},

  const  = {\ text}
}