Wolfgang Benz. "Opposition und Widerstand der Arbeiterbewegung" ("Opposition and Resistance of the Workers' Movement") Bundeszentrale für politische Bildung. Retrieved March 27, 2010. (in German)
Information about exhibit Foundation "Remembrance, Responsibility and Future", official website. (Parts of the site are in English, but the page about the exhibit is only in German.) Retrieved April 6, 2010 (in German)