@book { Sozialimmobilien,
    title = "Sozialimmobilien",
    author = "Anica {Pfaff}",
    year = "2001",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832444037",
    url = "https://m.diplom.de/document/220011"
}