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Non-simple purely infinite C*-algebras
- American Journal of Mathematics
- Johns Hopkins University Press
- Volume 122, Number 3, June 2000
- pp. 637-666
- 10.1353/ajm.2000.0021
- Article
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A C*-algebra A is defined to be purely infinite if there are no characters on A, and if for every pair of positive elements a, b in A, such that b lies in the closed two-sided ideal generated by a, there exists a sequence {rn} in A such that r*narn → b. This definition agrees with the usual definition by J. Cuntz when A is simple. It is shown that the property of being purely infinite is preserved under extensions, Morita equivalence, inductive limits, and it passes to quotients, and to hereditary sub-C*-algebras. It is shown that A ⊗ O∞ is purely infinite for every C*-algebra A. Purely infinite C*-algebras admit no traces, and, conversely, an approximately divisible exact C*-algebra is purely infinite if it admits no nonzero trace.