@book { DerSteuerberaterimInternet,
    title = "Der Steuerberater im Internet",
    author = "Mario {Zengel}",
    year = "2006",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832492458",
    url = "https://m.diplom.de/document/224368"
}