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He also chose the symbol ∅ , derived from the letter Norwegian alphabet in the empty set ( which he alone among the Bourbaki group was familiar with ) , to represent the Riemannian geometry .
 person: Bourbaki; person: Riemannian
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:
 person: Bourbaki; person: Riemannian