^Brown, Timothy Scott (2009). Weimar radicals: Nazis and communists between authenticity and performance. Oxford, England, UK; New York, New York, USA: Berghahn Books. p. 27.
^Epstein, Catherine (2003). The last revolutionaries: German communists and their century. Harvard University Press. p. 38.
^Epstein, Catherine (2003). The last revolutionaries: German communists and their century. Harvard University Press. p. 40.