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arXiv 1702.05628math.DS
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非常规阵列的遍历定理及Szemeredi定理的推广

Ergodic Theorems for Nonconventional Arrays and an Extension of the Szemeredi Theorem

Yuri Kifer

摘要:

本文主要研究具有$N^{-1}\sum_{n=1}^N\prod_{j=1}^\ell T^{P_j(n,N)}f_j$形式的非常规阵列的平均值作为$N\to\infty$的渐近行为,其中$f_j$是有界可测函数,$T$是可逆的保测度变换,$P_j$是$n$和$N$在整数上取整数值的多项式。结果表明,当$T$是弱混合且$P_j(n,N)=p_jn+q_jN$是线性的,或者更一般地,对于某些整数值多项式$P_j$和$Q_j$具有$P_j(n,N)=P_j(n)+Q_j(N)$的形式时,则上述平均值收敛于$L^2$,但是对于一般多项式$P_j$,即使在$\ell=1$的情况下,仅当$T$是强混合时,也可以确保$L^2$收敛。研究还弱混合和紧凑的扩展和依赖Furstenberg的结构定理,我们得出一个扩展Szemer\' edi的定理说,任何子集的整数$Λ$与积极的上密度存在一个子集$\mathcal N_Λ$的正整数具有一致有界的差距,使$N\in\mathcal N_Λ$和至少$\varepsilon N,\,\varepsilon>0$的$n$的所有数字$p_jn+q_jN,\, j=1,...,\ell$属于$Λ$。我们还获得了这些结果的一个版本的几个交换变换,从而产生相应的多维Szemer\' edi定理的扩展。

英文摘要:

The paper is primarily concerned with the asymptotic behavior as $N\to\infty$ of averages of nonconventional arrays having the form $N^{-1}\sum_{n=1}^N\prod_{j=1}^\ell T^{P_j(n,N)}f_j$ where $f_j$'s are bounded measurable functions, $T$ is an invertible measure preserving transformation and $P_j$'s are polynomials of $n$ and $N$ taking on integer values on integers. It turns out that when $T$ is weakly mixing and $P_j(n,N)=p_jn+q_jN$ are linear or, more generally, have the form $P_j(n,N)=P_j(n)+Q_j(N)$ for some integer valued polynomials $P_j$ and $Q_j$ then the above averages converge in $L^2$ but for general polynomials $P_j$ the $L^2$ convergence can be ensured even in the case $\ell=1$ only when $T$ is strongly mixing. Studying also weakly mixing and compact extensions and relying on Furstenberg's structure theorem we derive an extension of Szemer\' edi's theorem saying that for any subset of integers $Λ$ with positive upper density there exists a subset $\mathcal N_Λ$ of positive integers having uniformly bounded gaps such that for $N\in\mathcal N_Λ$ and at least $\varepsilon N,\,\varepsilon>0$ of $n$'s all numbers $p_jn+q_jN,\, j=1,...,\ell$ belong to $Λ$. We obtain also a version of these results for several commuting transformations which yields a corresponding extension of the multidimensional Szemer\' edi theorem.

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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