@book { Kundenkartenundclubs,
    title = "Kundenkarten und -clubs",
    author = "Thomas {Strelow}",
    year = "1999",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832418762",
    url = "https://m.diplom.de/document/217727"
}