@book { MarketingfrdenPNV,
    title = "Marketing für den ÖPNV",
    author = "Philip {Diekert}",
    year = "2003",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832468651",
    url = "https://m.diplom.de/document/222209"
}