@book { InternesundExternesRechnungswesen,
    title = "Internes und Externes Rechnungswesen",
    author = "Harald {Eichsteller} and Harald {Eichsteller}",
    year = "2012",
    publisher = "GRIN Verlag",
    address = "München, Germany",
    doi = "10.3239/9783656273707",
    url = "https://www.hausarbeiten.de/document/201514"
}