@book { TheodorBallauffRevolutionrpdagogischerDenkungsart,
    title = "Theodor Ballauff – «Revolutionär pädagogischer Denkungsart»",
    subtitle = "Ein Porträt",
    author = "Rudolf M. {Kühn}",
    year = "2007",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1101891"
}