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In 1812 , Ludwig van Beethoven conceived the idea of writing an opera about Attila and approached August von Kotzebue to write the libretto .
 Ludwig van Beethoven, Attila, August von Kotzebue
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Ludwig van Beethoven, Attila, August von Kotzebue