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From about 1955 he started to work on sheaf theory and homological algebra , producing the influential " Tôhoku paper " ( " Sur quelques points d'algèbre homologique " , published in the Tohoku Mathematical Journal in 1957 ) where he introduced abelian categories and applied their theory to show that sheaf cohomology can be defined as certain derived functors in this context .
 location: Tôhoku
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 location: Tôhoku