Definition:Ergodic Measure-Preserving Transformation/Definition 1

Definition
Let $\struct {X, \BB, \mu}$ be a probability space.

Let $T: X \to X$ be a measure-preserving transformation.

$T$ is said to be ergodic if for any $A \in \BB$:
 * $T^{-1} \sqbrk A = A \implies \map \mu A \in \set {0, 1}$

Also see

 * Equivalence of Defintions of Ergodic Measure-Preserving Transformation