[contravariant]

There are a couple of references, most on some obscure detail. The ones that might be worth a try for an introduction are:

- Walters, P., An Introduction to Ergodic Theory, Graduate Texts in Mathematics, 79. Springer-Verlag, New York-Berlin, 1982

- Billingsley, P. – Ergodic Theory and Information, John Wiley and Sons, 1965.

You may need a refresher on measure theory, or just ignore that part I suppose