@book { MarktgebietevonHandelsunternehmen,
    title = "Marktgebiete von Handelsunternehmen",
    author = "Jan {Harm}",
    year = "1997",
    publisher = "Diplom.de",
    address = "Hamburg, Germany",
    doi = "10.3239/9783832403034",
    url = "https://m.diplom.de/document/216288"
}