Necessity of approximate Kakutani structure for irreducible weighted shifts

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

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

and

1≤k≤n⇒∣αk−αcn,ϵ−k∣<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.

References

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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