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Robert Griess , who proved the existence of the monster in 1982 , has called those 20 groups the " happy family " , and the remaining six exceptions " pariahs " .
 Robert Griess
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Robert Griess