@book { RestnutzungsdauervonImmobilien,
    title = "Restnutzungsdauer von Immobilien",
    author = "Anett {Helff}",
    year = "2001",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832447083",
    url = "https://m.diplom.de/document/220312"
}