@book { Unternehmensberwachung,
    title = "Unternehmensüberwachung",
    author = "Carl-Christian {Freidank} and Remmer {Sassen}",
    year = "2013",
    publisher = "Vahlen",
    address = "München, Deutschland",
    url = "https://vahlen.openpublishing.com/document/1220891"
}