@book { CouponingimLebensmitteleinzelhandel,
    title = "Couponing im Lebensmitteleinzelhandel",
    author = "Michaela {Knümann}",
    year = "2003",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832472337",
    url = "https://m.diplom.de/document/222537"
}