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arXiv 1105.1979math.OA
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投射C* 代数的归纳极限

Inductive limits of projective C*-algebras

Hannes Thiel

摘要:

证明了可分C*-代数是投射C* 代数的归纳极限当且仅当它具有平凡形状,即当它与零C* 代数是形状等价的.特别地,每个可收缩C* 代数都是投射的归纳极限,并且可以假设连接同态是满射。有趣的是,Dadarlat的一个例子表明,平凡形状不会传递到完全遗传子C* 代数。因此,投射性也是如此。为了得到这些结果,我们发展了归纳极限分解的准则,并讨论了与不同逼近概念的关系。作为这些结果的一个主要应用,我们证明了一个C* 代数是(弱)投射的当且仅当它是(弱)半投射的且具有平凡形.因此,一个\ca{}是投射的当且仅当它是可收缩的和半投射的。这证实了洛林的一个猜想。

英文摘要:

We show that a separable C*-algebra is an inductive limits of projective C*-algebras if and only if it has trivial shape, that is, if it is shape equivalent to the zero C*-algebra. In particular, every contractible C*-algebra is an inductive limit of projectives, and one may assume that the connecting morphisms are surjective. Interestingly, an example of Dadarlat shows that trivial shape does not pass to full hereditary sub-C*-algebra. It then follows that the same fails for projectivity. To obtain these results, we develop criteria for inductive limit decompositions, and we discuss the relation with different concepts of approximation. As a main application of our findings we show that a C*-algebra is (weakly) projective if and only if it is (weakly) semiprojective and has trivial shape. It follows that a \ca{} is projective if and only if it is contractible and semiprojective. This confirms a conjecture of Loring.

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