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arXiv 1603.07720math.DSmath.CO
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Khintchine递归定理中的Under递归

Under recurrence in the Khintchine recurrence theorem

Michael Boshernitzan, Nikos Frantzikinakis, Máté Wierdl

摘要:

Khintchine递归定理断言,在保测度系统上,对于每一个集合$A$和$\varepsilon>0$,我们有$μ(A\cap T^{-n}A)\geq μ(A)^2-\varepsilon$对无限多个$n\in \mathbb{N}$。我们表明,有系统下的递归集$A$,在这个意义上,不等式$μ(A\cap T^{-n}A)< μ(A)^2$保持每$n\in \mathbb{N}$。特别地,所有正熵的遍历系统都有欠递归集。另一方面,回答V的问题。Bergelson,我们证明了不是所有的混合系统都有欠递归集。我们还研究了这些问题的变体,其中之前的严格不等式被逆转,并推断出欠重现是比过重现更罕见的现象。最后,我们研究了与多重递归相关的问题,并得到了一些有趣的组合结果。

英文摘要:

The Khintchine recurrence theorem asserts that on a measure preserving system, for every set $A$ and $\varepsilon>0$, we have $μ(A\cap T^{-n}A)\geq μ(A)^2-\varepsilon$ for infinitely many $n\in \mathbb{N}$. We show that there are systems having under-recurrent sets $A$, in the sense that the inequality $μ(A\cap T^{-n}A)< μ(A)^2$ holds for every $n\in \mathbb{N}$. In particular, all ergodic systems of positive entropy have under-recurrent sets. On the other hand, answering a question of V.~Bergelson, we show that not all mixing systems have under-recurrent sets. We also study variants of these problems where the previous strict inequality is reversed, and deduce that under-recurrence is a much more rare phenomenon than over-recurrence. Finally, we study related problems pertaining to multiple recurrence and derive some interesting combinatorial consequences.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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