English

Pointwise multiple averages for systems with two commuting transformations

Dynamical Systems 2017-02-09 v2

Abstract

We show that if (X,X,μ,S,T)(X,\mathcal{X},\mu,S,T) is an ergodic measure preserving system with commuting transformations SS and TT, then the average 1N3i,j,k=0N1f0(SjTkx)f1(Si+jTkx)f2(SjTi+kx)\frac{1}{N^3} \sum_{i,j,k=0}^{N-1} f_0(S^j T^k x) f_1 (S^{i+j} T^k x) f_2 (S^j T^{i+k} x) converges for μ\mu-a.e. xXx\in X as NN\to \infty for f0,f1,f2L(μ)f_0,f_1, f_2\in L^\infty(\mu). We also show that if (X,X,μ,S,T)(X,\mathcal{X},\mu,S,T) is a measurable distal system, the average 1Ni=0N1f1(Six)f2(Tix) \frac{1}{N}\sum_{i=0}^{N-1} f_1 (S^i x) f_2 (T^i x) converges for μ\mu-a.e. xXx\in X as NN\to \infty for f1,f2L(μ)f_1,f_2\in L^{\infty}(\mu).

Keywords

Cite

@article{arxiv.1509.09310,
  title  = {Pointwise multiple averages for systems with two commuting transformations},
  author = {Sebastian Donoso and Wenbo Sun},
  journal= {arXiv preprint arXiv:1509.09310},
  year   = {2017}
}

Comments

Some proofs clarified, following the referee's suggestions

R2 v1 2026-06-22T11:09:34.231Z