Lenin: 1908/mec: 3. L. Feuerbach and J. Dietzgen on the Thing-In-Itself https://www.marxists.org/archive/lenin/works/1908/mec/two3.htm
Archive_rosa_luxemburg-karl_liebknecht http://ciml.250x.com/archive/luxemburg-liebknecht/english/karl_liebknecht_self-determination_of_nations_and_self-defense_1918_english.html
Lenin: 1908/mec: 5. Absolute and Relative Truth, or the Eclecticism of Engels as Discovered by A. Bogdanov https://www.marxists.org/archive/lenin/works/1908/mec/two5.htm