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For a long time it was thought that he died during the Second Council of Lyon in 1274 or in 1275 , and shortly thereafter was succeeded in the see of Sabina by Giovanni Visconti , nephew of Gregory X. However , modern research has established that cardinal Giovanni Visconti never existed , while Bertrand is attested in the papal documents until the pontificate of John XXI ( 1276 – 77 ) .
 Lyon, Gregory, Bertrand, John XXI
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Lyon, Gregory, Bertrand, John XXI