@book { TextsortenundTextsortenvarianten,
    title = "Textsorten und Textsortenvarianten",
    author = "Karl-Ernst {Sommerfeldt}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1095332"
}