@book { KundenbindungvonFitnessunternehmen,
    title = "Kundenbindung von Fitnessunternehmen",
    author = "Roman {Schida}",
    year = "2001",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832434557",
    url = "https://m.diplom.de/document/219122"
}