@book { DiePrinzessinundderSchlssel,
    title = "Die Prinzessin und der Schlüssel",
    author = "David J. {Greening}",
    year = "2020",
    publisher = "Schreibstark-Verlag",
    address = ", Deutschland",
    url = "https://tolino.openpublishing.com/document/1014888"
}