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Even more significantly , at Heidelberg he became friends with another young Lutheran scholar , Carl Braaten , who would later become his " chief theological companion " and his most important theological collaborator .
 Heidelberg, Carl Braaten
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Heidelberg, Carl Braaten