Necessity of approximate Kakutani structure for irreducible weighted shifts

From papers

Let TT be an irreducible weighted shift with weights {αn}n=1\{\alpha_n\}_{n=1}^{\infty}. For each nNn\in\mathbb{N} and ϵ>0\epsilon>0, suppose there is an index cn,ϵnc_{n,\epsilon}\geq n such that

0<αcn,ϵ<ϵ,0<\alpha_{c_{n,\epsilon}}<\epsilon,

and

1knαkαcn,ϵk<ϵ.1\leq k\leq n\quad\Rightarrow\quad |\alpha_k-\alpha_{c_{n,\epsilon}-k}|<\epsilon.

Such a shift is called approximately Kakutani. The approximate Kakutani necessity conjecture. Every irreducible weighted shift in CSO\overline{\operatorname{CSO}} is approximately Kakutani. The preceding theorem proves that approximate Kakutani shifts belong to CSO\overline{\operatorname{CSO}}; the conjecture asserts the converse, giving a characterization of irreducible weighted shifts in the closure of the complex symmetric operators. Its status is not resolved in the supplied source.

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Primary source

Stephan Ramon Garcia and Daniel E. Poore, “On the closure of the complex symmetric operators: compact operators and weighted shifts”, arXiv:1106.4855 (2012).

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