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The corresponding extension problem for diffeomorphisms of higher-dimensional spheres " S " was much studied in the 1950 s and 1960 s , with notable contributions from René Thom , John Milnor and Stephen Smale .
 person: René Thom; person: John Milnor; person: Stephen Smale
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 person: René Thom; person: John Milnor; person: Stephen Smale