@book { SpitzenleistungenimKeyAccountManagement,
    title = "Spitzenleistungen im Key Account Management",
    author = "Christian {Belz} and Markus {Müllner} and Dirk {Zupancic}",
    year = "2021",
    publisher = "Vahlen",
    address = "München, Deutschland",
    url = "https://vahlen.openpublishing.com/document/1221392"
}