@book { Unbegrenzt,
    title = "Unbegrenzt",
    author = "Michael {Hofmann}",
    year = "2013",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    doi = "10.3726/978-3-653-03365-6",
    url = "https://www.peterlang.com/document/1046093"
}