@book { SeniorenundHandel,
    title = "Senioren und Handel",
    author = "Frank {Armbrust}",
    year = "1998",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832407780",
    url = "https://m.diplom.de/document/216685"
}