@book { WillyHellpach,
    title = "Willy Hellpach",
    author = "Walter {Stallmeister} and Helmut E. {Lück}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1079149"
}