@book { WillyHellpach18771955,
    title = "Willy Hellpach (1877-1955)",
    author = "Claudia-Anja {Kaune}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1099622"
}