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In the early 1970s he attended classes given by Cage , Ligeti , Stockhausen , and Xenakis at the Darmstadt Summer Courses , and by Ferrari and Kagel in Cologne .
 Cage, Ligeti, Stockhausen, Xenakis, Ferrari, Kagel, Cologne
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Cage, Ligeti, Stockhausen, Xenakis, Ferrari, Kagel, Cologne