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The economist Robin Hahnel has argued that free markets are in fact systematically inefficient because externalities are pervasive and because real-world markets are rarely truly competitive or in equilibrium .
 person: Robin Hahnel
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
 Entities: Robin Hahnel 
Answer:
 person: Robin Hahnel