@book { DieErklrungvonGruppenprozessen,
    title = "Die Erklärung von Gruppenprozessen",
    author = "Hans {Lechner}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1090708"
}