@book { JohannesVIII,
    title = "Johannes VIII.",
    subtitle = "Päpstliche Herrschaft in den karolingischen Teilreichen am Ende des 9. Jahrhunderts",
    author = "Dorothee {Arnold}",
    year = "2005",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1098290"
}