@book { WalthervonderVogelweide,
    title = "Walther von der Vogelweide",
    subtitle = "Untersuchungen zur Varianz in der Liedüberlieferung",
    author = "Elmar {Willemsen}",
    year = "2006",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1101084"
}