@book { HerstellervsHndlermarken,
    title = "Hersteller- vs. Händlermarken",
    author = "Jan Wilhelm {Wittig}",
    year = "2010",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836647977",
    url = "https://m.diplom.de/document/227832"
}