1. A. Katok, Lyapunov exponents, entropy and periodic orbits for diffeomorphisms, Publ.Math.I.H.E.S., v.51(1980), 137–173.
2. P. Billingsley, Ergodic Theory and Information, New York, John Wiley, 1965.
3. A.Katok, Hyperbolicity in smooth dynamical systems, Ecole d'eté de Physique Theorique, Les Houches, 1981, Proc., to appear.