https://digital.katalog.queersearch.org/s/katalog/item/64190, “Gesammelte Briefe. Band VI. 1938-1940”, https://digital.katalog.queersearch.org/s/katalog/item/47512, QueerSearch, accessed 15. März 2025, https://digital.katalog.queersearch.org/s/katalog/item/28871