@book { SystemederAltersversorgunginDeutschland,
    title = "Systeme der Altersversorgung in Deutschland",
    author = "Kristin {Pehl}",
    year = "2007",
    publisher = "Diplom.de",
    address = "Hamburg, Germany",
    doi = "10.3239/9783836604741",
    url = "https://m.diplom.de/document/228968"
}