@book { DeutschinEuropa,
    title = "Deutsch in Europa",
    subtitle = "Muttersprache und Fremdsprache",
    author = "Ingrid {Kühn} and Marianne {Lehker}",
    year = "2002",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1093049"
}