@book { GeschichtederVorschulerziehung,
    title = "Geschichte der Vorschulerziehung",
    author = "Jürgen {Schäfer}",
    year = "1987",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1076566"
}