@book { ZickzackLernen,
    title = "Zickzack-Lernen",
    author = "Gerhard {Schaefer} and Regina {Manitz-Schaefer}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1093040"
}