\[ \newcommand{\C}{\mathbb{C}} \newcommand{\haar}{\mathsf{m}} \newcommand{\P}{\mathcal{P}} \newcommand{\R}{\mathbb{R}} \newcommand{\N}{\mathbb{N}} \newcommand{\Z}{\mathbb{Z}} \newcommand{\d}{\mathsf{d}} \newcommand{\g}{>} \newcommand{\l}{<} \newcommand{\intd}{\,\mathsf{d}} \newcommand{\Re}{\mathsf{Re}} \newcommand{\area}{\mathop{\mathsf{Area}}} \newcommand{\met}{\mathop{\mathsf{d}}} \newcommand{\emptyset}{\varnothing} \newcommand{\B}{\mathscr{B}} \newcommand{\fou}{\mathcal{F}} \]

Week 5 Tutorial

Fix an irrational number $\alpha$ and put \[ T(x) = x + \alpha \bmod 1 \] for all $x \in [0,1)$.

  1. Is there $n \in \N$ with $0 \l T^n(0) \l \tfrac{1}{4}$?
  2. Is there $n \in 2\N$ with $0 \l T^n(0) \l \tfrac{1}{4}$?
  3. Is there $n \in 2\N+1$ with $0 \l T^n(0) \l \tfrac{1}{4}$?
  4. Is there $0 \le n \le 3$ with $0 \l T^n(0) \l \tfrac{1}{4}$?
  5. Is there $0 \le n \le 7^{1000}$ with $0 \l T^n(0) \l \tfrac{1}{4}$?
  6. Is there $0 \le n \le 3$ with $-\tfrac{1}{8} \l T^n(0) \l \tfrac{1}{8}$?
  7. Is there $0 \le n \le 7^{1000}$ with $-\tfrac{1}{8} \l T^n(0) \l \tfrac{1}{8}$?
  1. Give an example of a set $E \subset [0,1)$ with \[ \lim_{N \to \infty} \dfrac{1}{N} \sum_{n=0}^{N-1} 1_E(T^n(x)) = 0 \] and $\lambda(E) = 1$.
  2. Give an example of a set $E \subset [0,1)$ for which \[ \lim_{N \to \infty} \dfrac{1}{N} \sum_{n=0}^{N-1} 1_E(T^n(x)) \] does not exist.
  3. A continuous function $f : [0,1) \to [0,\infty)$ is such that \[ \lim_{N \to \infty} \dfrac{1}{N} \sum_{n=0}^{N-1} f(T^n(x)) = 0 \] holds. What can you say about $f$?