@book { EinPersonenUnternehmen,
    title = "Ein-Personen-Unternehmen",
    author = "Armin {Wenny}",
    year = "1999",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783832414566",
    url = "https://m.diplom.de/document/217307"
}