Spatial-temporal differentiation theorems

Abstract

Let $(X, \mathcal{B}, \mu, T)$ be a dynamical system where X is a compact metric space with Borel $\sigma$-algebra $\mathcal{B}$, and $\mu$ is a probability measure that is ergodic with respect to the homeomorphism $T \colon X \to X$. We study the following differentiation problem: Given $f \in C(X)$ and $F_k \in \mathcal{B}$, where $\mu(F_k) > 0$ and $\mu(F_k) \to 0$, when can we say that

$$\lim_{k \to \infty} \frac{\int_{F_k} ( \frac{1}{k} \sum_{i = 0}^{k - 1} T^i f ) \, \, \mathrm{d} \mu}{\mu(F_k)} = \int f \, \mathrm{d} \mu \ ?$$

We establish some sufficient conditions for these sequences to converge.