@book { SekundrzweckeimVergaberecht,
    title = "Sekundärzwecke im Vergaberecht",
    author = "Gerald {Scharpenack}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1099414"
}