@book { AlterssicherungundIndividualprinzip,
    title = "Alterssicherung und Individualprinzip",
    author = "Matthias {Ries}",
    year = "1997",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832402471",
    url = "https://m.diplom.de/document/216192"
}