@book { GeschftskorrespondenzvonAZ,
    title = "Geschäftskorrespondenz von A - Z",
    author = "Gabi {Neumayer} and Ulrike {Rudolph}",
    year = "2011",
    publisher = "humboldt",
    address = "Hannover, Deutschland",
    url = "https://schluetersche.openpublishing.com/document/403365"
}