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Real Af C*-Algebras With K0 of Small Rank

Published online by Cambridge University Press:  20 November 2018

T. Giordano  and
D. E. Handelman
T. Giordano
Affiliation:
Université de Genève, Genève, Switzerland
D. E. Handelman
Affiliation:
University of Ottawa, Ottawa, Ontario
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A real AF C*-algebra is the norm closure of a direct limit of finite dimensional real C*-algebras (with real *-algebra maps). When we use the unadorned “AF C*-algebra”, we mean the usual complex version.

Let R be a simple AF C*-algebra such that K0(R) is free of rank 2 or 3. The problem is to find (up to Morita equivalence) all real AF C*-algebras A such that AꕕC≅R. This is closely related to the problem of finding all involutions on R [3], [10].

For example, when the rank is 2, generically there are 8 such classes. The exceptional cases arise when the ratio of the two generators in K0(R) is a quadratic (algebraic) number, and here there are 4, 5, or 8 Morita equivalence classes, the number depending largely on the behaviour of the prime 2 in the relevant algebraic number field.

Type
Research Article
Information
Canadian Journal of Mathematics , Volume 41 , Issue 5 , 01 October 1989 , pp. 786 - 807
Copyright
Copyright © Canadian Mathematical Society 1989

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