Let $M = (X, \mathcal{F}, \mu, T)$ be a D2827: Measure-preserving system such that

(i)	$E \in \mathcal{F}$ is a D1109: Measurable set in $M$

Then \begin{equation} \forall \, n \in \mathbb{N} : \mu(T^{-n} E) = \mu(E) \end{equation}