Rod Hay asks for a reference for my summary of Marx's theory of   
exploitation as: "all value derives from labor and not giving labor all   
of production amounts to exploitation."   I'll look for one the next   
time I'm in my office.  
  
Meanwhile, Rod may look up a table in Ekelund and Hebert's History of   
Economic Theory and Analysis (if I recall the title correctly) used to   
illustrate Marx's attempt to explain deviations between values and   
prices in different sectors of an economy.  The same chapter explains   
Marx's theory of exploitation, pretty much as restated in Warren   
Samuels's last post.  
  
James Ahiakpor