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A remark on the ultrapower algebra of the hyperfinite factor
Journal article   Open access   Peer reviewed

A remark on the ultrapower algebra of the hyperfinite factor

Ionut Chifan and Sayan Das
Proceedings of the American Mathematical Society, Vol.146(12), pp.5289-5294
12/01/2018
DOI: 10.1090/proc/14197
url
https://doi.org/10.1090/proc/14197View
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Abstract

On page 43 in [Adv. in Math. 50 (1983), pp. 27–48] Sorin Popa asked whether the following property holds: If ω\omega is a free ultrafilter on N\mathbb N and R1⊆R\mathcal {R}_1\subseteq \mathcal {R} is an irreducible inclusion of hyperfinite II1_1 factors such that R′∩Rω⊆R1ω\mathcal {R}’\cap \mathcal {R}^\omega \subseteq \mathcal {R}^\omega _1 does it follows that R1=R\mathcal {R}_1=\mathcal {R}? In this short note we provide an affirmative answer to this question.
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