@book { DerSanierungsplan,
    title = "Der Sanierungsplan",
    author = "Christian {Konen}",
    year = "2002",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832456627",
    url = "https://m.diplom.de/document/221142"
}