Let $(X, \mathscr{B}(X), P)$ be a probability space and let $T$ be a $K$-automorphism. If $T$ satisfies a Rosenblatt mixing condition of a certain kind, we show that if $\{k_n\}^\infty_{n=1}$ is an arbitrary increasing sequence of integers and $g$ belongs to a certain class of functions then $$\lim_{n\rightarrow\infty} \frac{1}{n} \sum^n_{j=1} g(T^{k_j}x) = E(g) \mathrm{a.s.}$$
@article{1176995857,
author = {Blum, J. R. and Reich, J. I.},
title = {On the Individual Ergodic Theorem for $K$-Automorphisms},
journal = {Ann. Probab.},
volume = {5},
number = {6},
year = {1977},
pages = { 309-314},
language = {en},
url = {http://dml.mathdoc.fr/item/1176995857}
}
Blum, J. R.; Reich, J. I. On the Individual Ergodic Theorem for $K$-Automorphisms. Ann. Probab., Tome 5 (1977) no. 6, pp. 309-314. http://gdmltest.u-ga.fr/item/1176995857/