@book { DieDiskussionzurGreencard,
    title = "Die Diskussion zur Greencard",
    author = "Thomas {Reichel}",
    year = "2002",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832450397",
    url = "https://m.diplom.de/document/220189"
}