Surplus value and exploitation

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On the labour theory of value...
From a discussion in the alt.politics.communism newsgroup, 30 June 2006. Haines Brown argues that value is not simply an empirical quantity, but is a causal relation.
Two questions related to marxist theory
Part of a dialog on the list, 8 March 2007. Question: Does anyone know of a marxist explanation of what the Labour Theory of Value says about the relationship between energy and value? The reply draws upon thermodynamics.