https://digital.katalog.queersearch.org/s/katalog/item/43324, “Der junge Engels und die Berliner Universität 1837-1842”, https://digital.katalog.queersearch.org/s/katalog/item/49456, QueerSearch, accessed 1. Mai 2025, https://digital.katalog.queersearch.org/s/katalog/item/26028