@book { DerinternationaleGelegenheitsLuftverkehr,
    title = "Der internationale «Gelegenheits»Luftverkehr",
    author = "Wolfdieter {Diersch}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1071666"
}