@book { GesunderSchlaf,
    title = "Gesunder Schlaf",
    author = "Dr. med. Guido {Ern} and Dr. med. Ralf D. {Fischbach}",
    year = "2010",
    publisher = "humboldt",
    address = "Hannover, Deutschland",
    url = "https://schluetersche.openpublishing.com/document/403392"
}