@book { DerholsteinischeAdelimHochmittelalter,
    title = "Der holsteinische Adel im Hochmittelalter",
    author = "Hans Gerhard {Risch}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1135576"
}