Abstract:
Let $\overline{\mathfrak{S}}_\infty$ denote the set of all bijections of natural numbers. Consider an action of $\overline{\mathfrak{S}}_\infty$ on a measure space$\left( X,\mathfrak{M},\mu \right)$, where $\mu$ is an $\overline{\mathfrak{S}}_\infty$-quasi-invariant measure. We prove that there exists an $\overline{\mathfrak{S}}_\infty$-invariant measure equivalent to $\mu$.
Key words and phrases:full symmetric group, nonsingular automorphism, Koopman representation, invariant measure.