The existence of a simple nuclear algebra with identical scaled projection semigroups but no matrix isomorphism

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Let AA be a simple, unital, separable, and nuclear C∗C^*-algebra of stable rank one. Write V(A)V(A) for its Murray–von Neumann semigroup of projections and [1A][1_A] for the class of its unit. Counterexample to Elliott's classification conjecture. There exists such an algebra AA for which

A≆Mn(A)for some n∈N,A \ncong \mathrm{M}_n(A) \quad\text{for some } n\in\mathbb{N},

yet

(V(A),[1A])≅(V(Mn(A)),[1Mn(A)])≅(Q+,1).(V(A),[1_A])\cong (V(\mathrm{M}_n(A)),[1_{\mathrm{M}_n(A)}])\cong (\mathbb{Q}^+,1).

This provides a particularly strong counterexample to Elliott's classification conjecture for simple, separable, nuclear C∗C^*-algebras, since the scaled ordered projection semigroup does not distinguish AA from a matrix algebra over AA.

References

Primary source

Andrew S. Toms, “Flat dimension growth for C*-algebras”, arXiv:math/0510409 (2006).

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