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| Format: | Preprint |
| Published: |
2025
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| Online Access: | https://arxiv.org/abs/2506.21421 |
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| _version_ | 1866913914291224576 |
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| author | Young, Aidan |
| author_facet | Young, Aidan |
| contents | We show that if $(X, μ, T)$ is a probability measure-preserving dynamical system, and $\mathscr{P}$ is a countable partition of $(X, μ)$, then the limit $$ \lim_{n, k \to \infty} \mathbb{E} \left[ \frac{1}{k} \sum_{j = 0}^{k - 1} f \circ T^j \mid \bigvee_{i = 0}^{n - 1} T^{-i} \mathscr{P} \right] $$ exists almost surely for all $f \in L^p(μ), p > 1$. We prove this as a corollary of a geometric result: that if $(X, μ)$ is a metric measure space on which the Hardy-Littlewood maximal inequality holds, then the limit $$\lim_{r \searrow 0, k \to \infty} μ(B(x, r))^{-1} \int_{B(x, r)} \frac{1}{k} \sum_{j = 0}^{k - 1} f \circ T^j \mathrm{d} μ$$ exists almost surely. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2506_21421 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | An ergodic Lebesgue differentiation theorem Young, Aidan Dynamical Systems We show that if $(X, μ, T)$ is a probability measure-preserving dynamical system, and $\mathscr{P}$ is a countable partition of $(X, μ)$, then the limit $$ \lim_{n, k \to \infty} \mathbb{E} \left[ \frac{1}{k} \sum_{j = 0}^{k - 1} f \circ T^j \mid \bigvee_{i = 0}^{n - 1} T^{-i} \mathscr{P} \right] $$ exists almost surely for all $f \in L^p(μ), p > 1$. We prove this as a corollary of a geometric result: that if $(X, μ)$ is a metric measure space on which the Hardy-Littlewood maximal inequality holds, then the limit $$\lim_{r \searrow 0, k \to \infty} μ(B(x, r))^{-1} \int_{B(x, r)} \frac{1}{k} \sum_{j = 0}^{k - 1} f \circ T^j \mathrm{d} μ$$ exists almost surely. |
| title | An ergodic Lebesgue differentiation theorem |
| topic | Dynamical Systems |
| url | https://arxiv.org/abs/2506.21421 |