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In fact , Rincewind 's head holds one of the eight spells from the Octavo , the most powerful spellbook in the Discworld , and he has been unable to learn others because " they were afraid to be in the same head " as the Octavo spell .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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