@book { VariationinSprachtheorieundSpracherwerb,
    title = "Variation in Sprachtheorie und Spracherwerb",
    author = "Maurice {Vliegen}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1101128"
}