@book { ProudhonBibliographie,
    title = "Proudhon - Bibliographie",
    author = "Johannes {Hilmer} and Lutz {Roemheld}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1076977"
}