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He began by extending Karl Schwarzschild 's earlier work on radiation pressure in Emden polytropic models .
 person: Karl Schwarzschild; person: Emden
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: Karl Schwarzschild; person: Emden