@book { DerRuhetag,
    title = "Der Ruhetag",
    subtitle = "Sinngehalte einer fast vergessenen Gottesgabe",
    author = "",
    year = "1981",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1072106"
}