@book { FritzHelling18881973SchriftenRedenundBriefe,
    title = "Fritz Helling (1888-1973). Schriften, Reden und Briefe",
    author = "Jürgen {Sprave}",
    year = "2020",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    doi = "10.3726/b17899",
    url = "https://www.peterlang.com/document/1111548"
}