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Michio Kaku and Keiji Kikkawa gave a different formulation of the bosonic string , as a string field theory , with infinitely many particle types and with fields taking values not on points , but on loops and curves .
 person: Michio Kaku; person: Keiji Kikkawa
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 person: Michio Kaku; person: Keiji Kikkawa