https://digital.katalog.queersearch.org/s/katalog/item/41821, “Die frühe Homosexuellenbewegung 1864-1935”, https://digital.katalog.queersearch.org/s/katalog/item/48403, QueerSearch, accessed 29. April 2025, https://digital.katalog.queersearch.org/s/katalog/item/26386