Lenin: Postscript to the Article 'The Debate on the Extension of the Duma's Budgetary Powers' https://www.marxists.org/archive/lenin/works/1908/mar/26.htm
Doctoral Dissertation of Karl Marx — Chapter 2 https://marxistleninists.org/M&E/1841/dr-theses/ch02.htm
Doctoral Dissertation of Karl Marx — Chapter 3 https://marxistleninists.org/M&E/1841/dr-theses/ch03.htm
First International Archive http://ciml.250x.com/archive/international1/english/engels_1878_working_men_of_europe_in_1877.html