Invariant measures and equilibrium states for some mappings which expand distances

For a certain collection of transformations T we define a Perron-Frobenius operator and prove a convergence theorem for the powers of the operator along the lines of the theorem D. Ruelle proved in his investigation of the equilibrium states of one-dimensional lattice systems. We use the convergence theorem to study the existence and ergodic properties of equilibrium states for T and also to study the problem of invariant measures for T . Examples of the transformations T considered are expanding maps, transformations arising from f -expansions and shift systems.