@book { JohannesHeckel,
    title = "Johannes Heckel",
    subtitle = "Leben und Wirken (1889 -1963)",
    author = "Gisela {Emling}",
    year = "2011",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1108090"
}