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Huygens , who was , along with Leibniz , a neo-Cartesian and critic of Newton , concluded after a long correspondence that Leibniz 's writings on celestial mechanics made no sense , and that his invocation of a harmonic vortex was logically redundant , because Leibniz 's radial equation of motion follows trivially from Newton 's laws .
 Huygens, Leibniz, Newton, Leibniz, Leibniz, Newton
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Huygens, Leibniz, Newton, Leibniz, Leibniz, Newton