@book { VariettenTheorieundEmpirie,
    title = "Varietäten – Theorie und Empirie",
    author = "Alexandra N. {Lenz} and Klaus J. {Mattheier}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1099634"
}