@book { OffenerUnterricht,
    title = "Offener Unterricht",
    author = "Paula {Svoboda}",
    year = "2009",
    publisher = "GRIN Verlag",
    address = "München, Germany",
    doi = "10.3239/9783640500949",
    url = "https://www.hausarbeiten.de/document/139849"
}