https://digital.katalog.queersearch.org/s/katalog/item/64190, “Gesammelte Briefe. Band III. 1925-1930”, https://digital.katalog.queersearch.org/s/katalog/item/47512, QueerSearch, accessed 15. März 2025, https://digital.katalog.queersearch.org/s/katalog/item/28870