@book { GanzheitlichesGehirntrainingbungsbuch2,
    title = "Ganzheitliches Gehirntraining Übungsbuch 2",
    author = "Ursula {Oppolzer}",
    year = "2018",
    publisher = "Schlütersche Verlagsgesellschaft mbH & Co. KG",
    address = ", Deutschland",
    url = "https://schluetersche.openpublishing.com/document/404169"
}