Engels, Friedrich. 1972. ”Engels to J. Bloch in Königsberg: London, September 21, 1890.” Ote teoksesta Historical Materialism (Marx, Engels, Lenin), 294–296. www.marxists.org/archive/marx/works/1890/letters/90_09_21.htm
Engels, Friedrich. 1972. ”Engels to J. Bloch in Königsberg: London, September 21, 1890.” Ote teoksesta Historical Materialism (Marx, Engels, Lenin), 294–296. www.marxists.org/archive/marx/works/1890/letters/90_09_21.htm