Articles by Frederick Engels in The Northern Star https://marxistleninists.org/M&E/1845/10/index.htm
Lenin: 1905/3rdcong: Speech on the Procedure of the Discussion of the Resolutions on the Relations Between Workers and Intellectuals within the Social-Democratic Organisations https://www.marxists.org/archive/lenin/works/1905/3rdcong/21.htm
Economic Manuscripts: Grundrisse: p 201 - p 238 http://hiaw.org/defcon6/works/1857/grundrisse/ch04.html