@book { NonPerformingLoansinDeutschland,
    title = "Non-Performing Loans in Deutschland",
    author = "Ulrich {Bitterling}",
    year = "2008",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836617369",
    url = "https://m.diplom.de/document/226040"
}