@book { DieGruppealsderMenschimPlural,
    title = "Die Gruppe als «der Mensch im Plural»",
    subtitle = "Die Gruppenpädagogik Magda Kelbers",
    author = "Kurt {Frey}",
    year = "2003",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1095445"
}