@book { RatgeberAdipositasOP,
    title = "Ratgeber Adipositas-OP",
    author = "Prof. Dr. med. Stefan {Schopf}",
    year = "2023",
    publisher = "humboldt",
    address = "Hannover, Deutschland",
    url = "https://schluetersche.openpublishing.com/document/1319876"
}