@book { DieZusageimUmsatzsteuerrecht,
    title = "Die Zusage im Umsatzsteuerrecht",
    author = "Max {Weber}",
    year = "2019",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    doi = "10.3726/b15114",
    url = "https://www.peterlang.com/document/1057499"
}