This book is about discrete-time, time-homogeneous, Markov chains (Mes)
and their ergodic behavior. To this end, most of the material is in fact
about stable Mes, by which we mean Mes that admit an invariant
probability measure. To state this more precisely and give an overview
of the questions we shall be dealing with, we will first introduce some
notation and terminology. Let (X, B) be a measurable space, and consider
a X-valued Markov chain . = { k' k = 0, 1, ... } with transition
probability function (t.pJ.) P(x, B), i.e., P(x, B): = Prob ( k+1 E B I
k = x) for each x E X, B E B, and k = 0,1, .... The Me . is said to be
stable if there exists a probability measure (p.m.) /.l on B such that
(*) VB EB. /.l(B) = Ix /.l(dx) P(x, B) If (*) holds then /.l is called
an invariant p.m. for the Me . (or the t.p.f. P).