@book { Kundenrckgewinnung,
    title = "Kundenrückgewinnung",
    subtitle = "Sieben Prinzipien zum Erfolg",
    author = "Carlo {Morhard}",
    year = "2011",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783842815261",
    url = "https://m.diplom.de/document/228522"
}