Let $S = (\Omega, \mathcal{F}, \mathbb{P}, T)$ be a D2839: Probability-preserving system.
An D1716: Event $E \in \mathcal{F}$ in $(\Omega, \mathcal{F}, \mathbb{P})$ is stationary with respect to $T$ if and only if \begin{equation} T^{-1} E = E \end{equation}