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In the early 1980 s , a combination of results due to Simon Donaldson and Michael Freedman led to the discovery of exotic " R " s : there are uncountably many pairwise non-diffeomorphic open subsets of " R " each of which is homeomorphic to " R " , and also there are uncountably many pairwise non-diffeomorphic differentiable manifolds homeomorphic to " R " that do not embed smoothly in " R " .
 person: Simon Donaldson; person: Michael Freedman
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: Simon Donaldson; person: Michael Freedman