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Nonetheless , some of his views on the idea of flat taxation remained , albeit altered in the third edition of the " Principles of Political Economy " to reflect a concern for differentiating restrictions on " unearned " incomes , which he favoured , and those on " earned " incomes , which he did not favour .
 None
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 None