@book { DerLeistungsbegriffimArbeitsverhltnis,
    title = "Der Leistungsbegriff im Arbeitsverhältnis",
    author = "Gernot {Müller}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1069683"
}