On the magic square C*-algebra of size 4

Takeshi Katsura, Masahito Ogawa, Airi Takeuchi

Research output: Contribution to journalArticlepeer-review


In this paper, we investigate the structure of the magic square C*-algebra A(4) of size 4. We show that a certain twisted crossed product of A(4) is isomorphic to the homogeneous C*-algebra M4 (FORMULA PRESENT (RP3 )). Using this result, we show that A(4) is isomorphic to the fixed point algebra of M4 (C (RP3 )) by a certain action. From this concrete realization of A(4), we compute the K-groups of A(4) and their generators.

Original languageEnglish
Pages (from-to)99-148
Number of pages50
JournalAnnales Mathematiques Blaise Pascal
Issue number1
Publication statusPublished - 2022


  • 46L55
  • 46L80
  • C*-algebra
  • K-theory. 2020 Mathematics Subject Classification: 46L05
  • magic square C*-algebra
  • twisted crossed product

ASJC Scopus subject areas

  • Analysis
  • Algebra and Number Theory
  • Geometry and Topology
  • Applied Mathematics


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