@book { DasgroeBuchderMusterbriefe,
    title = "Das große Buch der Musterbriefe",
    author = "Claudia {Marbach} and Eike {Hovermann}",
    year = "2016",
    publisher = "humboldt",
    address = "Hannover, Deutschland",
    url = "https://schluetersche.openpublishing.com/document/403361"
}