@book { DiehistorischeEntwicklungdesRechtsinstitutsVerwaltungsakt,
    title = "Die historische Entwicklung des Rechtsinstituts Verwaltungsakt",
    author = "Markus {Engert}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1094118"
}