@book { DerRkstein,
    title = "Der Rökstein",
    subtitle = "Über die religiöse Bestimmung und das weltliche Schicksal eines Helden aus der frühen Wikingerzeit",
    author = "John Ole {Askedal} and Ottar {Grönvik}",
    year = "2003",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1096049"
}