Classification conjecture for ultraproducts of matrix algebras

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Let (ni)i→θ(n_i)_{i\to\theta} and (mj)j→θ′(m_j)_{j\to\theta'} be families of natural numbers, and let θ\theta and θ′\theta' be ultrafilters. Write τ\tau for the corresponding ultralimit of residues modulo dd. Ultraproduct classification conjecture.

∏UMni≡∏V⁡Mmjif and only iflim⁡Uni mod d=lim⁡Vmi mod dfor all d∈N.\prod_\mathcal{U} M_{n_i} \equiv \prod_{\operatorname{\mathcal{V}}} M_{m_j} \qquad \text{if and only if} \qquad \lim_\mathcal{U} n_i \bmod d = \lim_{\mathcal{V}} m_i \bmod d \quad \text{for all } d \in \mathbb{N}.

This proposes that the equivalence of ultraproducts of finite-dimensional matrix algebras is completely determined by the limiting residue classes of their matrix sizes modulo every natural number. The surrounding discussion concerns structural decompositions of pseudocompact and pseudomatrical C∗C^*-algebras; the supplied text does not establish the conjecture or indicate whether it has been resolved.

References

Primary source

Stephen Hardy, “Pseudocompact C^*-algebras”, arXiv:1609.06275 (2016).

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