@book { Stadtluftmachtfrei,
    title = "Stadtluft macht frei",
    subtitle = "Von der Polis zur Cyberstadt- Philosophische Auseinandersetzungen",
    author = "Fernand {Guelf}",
    year = "2009",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1107019"
}