@book { DerwiderspenstigeKlassiker,
    title = "Der widerspenstige Klassiker",
    author = "Klaus-Dieter {Ertler} and Andrea Maria {Humpl}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1102754"
}