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This approach was continued by Russell and Whitehead in their influential " Principia Mathematica " , first published 1910 – 1913 , and with a revised second edition in 1927 .
 Russell, Whitehead
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Russell, Whitehead