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and he is sometimes called the first of the three " novas " of 20th - century science fiction ( with Stanley G. Weinbaum and Robert A. Heinlein as the second and third novas ) .
 Stanley G. Weinbaum, Robert A. Heinlein
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Stanley G. Weinbaum, Robert A. Heinlein