Let $X$ be the circle $\mathbb{R}/\mathbb{Z}$ and let $R_{\theta}(x) = x + \theta$ mod $1$ be the rotation by an irrational angle $\theta$. Prove that the Lebesgue measure $\mu$ is ergodic.
This is taken from Foundations of ergodic theory by Viana and Oliveira. I have found a few different proof...