@book { GrundzgederlandwirtschaftlichenMarktlehre,
    title = "Grundzüge der landwirtschaftlichen Marktlehre",
    author = "Ulrich {Koester}",
    year = "2016",
    publisher = "Vahlen",
    address = "München, Deutschland",
    url = "https://vahlen.openpublishing.com/document/1220956"
}