@book { RandgruppenimMittelalter,
    title = "Randgruppen im Mittelalter",
    author = "Marco {Müller}",
    year = "2004",
    publisher = "GRIN Verlag",
    address = "München, Germany",
    doi = "10.3239/9783638275583",
    url = "https://www.hausarbeiten.de/document/24763"
}