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arXiv 1002.2028math.COmath.DS
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一个算术正则性引理、相关计数引理及其应用

An arithmetic regularity lemma, associated counting lemma, and applications

Ben Green, Terence Tao

摘要:

Szemeredi的正则性引理可以被看作是任意稠密图的粗糙结构定理,将这样的图分解为结构化的部分(划分为具有边缘密度的单元),小误差(对应于不规则单元)和均匀部分(与边缘密度的伪随机偏差)。我们建立了一个算术正则性引理,类似地将有界函数f:[N] -> C分解为一个(均匀分布的,虚拟的)-步零序列,一个在L^2中很小的误差和一个在Gowers U^{s+1}-范数中很小的误差,其中s是正整数。然后,我们建立了一个互补的算术计数引理,计数的算术模式的nilsequence分量的f。我们提供了一些应用这些引理:证明Szemeredi定理的等差数列,证明了一个猜想的Bergelson,主机和克拉,并概括了某些结果的Gowers和狼。我们的结果依赖于作者和T.齐格勒2020年11月修订:本文已被修订,因此计数引理仅涵盖满足称为标志性质的条件的线性型系统。平移不变系统,以及柯西-施瓦茨复杂度为1的系统和其他一些自然发生的系统都具有这个性质。我们感谢丹尼尔·奥尔特曼提请我们注意什么似乎是一个小的技术问题在我们的证明之一,但最终导致我们意识到,计数引理失败相当严重(相当简单的例子,我们将描述)没有一些假设这种类型。此外,我们还提供了一个简短的附录,说明系统的Gowers-Wolf复杂性受其Cauchy-Schwarz复杂性的限制。

英文摘要:

Szemeredi's regularity lemma can be viewed as a rough structure theorem for arbitrary dense graphs, decomposing such graphs into a structured piece (a partition into cells with edge densities), a small error (corresponding to irregular cells), and a uniform piece (the pseudorandom deviations from the edge densities). We establish an arithmetic regularity lemma that similarly decomposes bounded functions f : [N] -> C, into a (well-equidistributed, virtual) -step nilsequence, an error which is small in L^2 and a further error which is miniscule in the Gowers U^{s+1}-norm, where s is a positive integer. We then establish a complementary arithmetic counting lemma that counts arithmetic patterns in the nilsequence component of f. We provide a number of applications of these lemmas: a proof of Szemeredi's theorem on arithmetic progressions, a proof of a conjecture of Bergelson, Host and Kra, and a generalisation of certain results of Gowers and Wolf. Our result is dependent on the inverse conjecture for the Gowers U^{s+1} norm, recently established for general s by the authors and T. Ziegler. REVISED November 2020: This paper has been revised so that only systems of linear forms satisfying a condition called the flag property are covered by the counting lemma. Translation-invariant systems, as well as systems of Cauchy-Schwarz complexity 1 and some other naturally-occurring systems have this property. We thank Daniel Altman for drawing our attention to what appeared to be a minor technical issue in one of our proofs but which ultimately led us to realise that the the counting lemma fails quite badly (with rather simple examples, which we shall describe) without some assumption of this type. Additionally, we supply a short appendix showing that the Gowers-Wolf complexity of a system is bounded by its Cauchy-Schwarz complexity.

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