@book { WolframvonEschenbachWillehalm,
    title = "Wolfram von Eschenbach 'Willehalm'",
    author = "Peter {Heilek}",
    year = "2009",
    publisher = "GRIN Verlag",
    address = "München, Germany",
    doi = "10.3239/9783640363926",
    url = "https://www.hausarbeiten.de/document/130561"
}