@book { ImmobilienalsMittelderprivatenAltersvorsorge,
    title = "Immobilien als Mittel der privaten Altersvorsorge",
    author = "Andreas {Vorbauer}",
    year = "2003",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832463205",
    url = "https://m.diplom.de/document/221762"
}