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Carl Friedrich Gauss had earlier published an essentially topological proof of the theorem in 1797 but expressed his doubts at the time about " the true metaphysics of the square root of − 1 " .
 Carl Friedrich Gauss
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Carl Friedrich Gauss