@book { MarketingundVertriebsrecht,
    title = "Marketing- und Vertriebsrecht",
    author = "Axel {Birk} and Joachim {Löffler} and Sabine {Boos}",
    year = "2020",
    publisher = "Vahlen",
    address = "München, Deutschland",
    url = "https://vahlen.openpublishing.com/document/1222731"
}