Markov process is a process with one step memory, i$.$e$.,$ a process such that p$($xn$|$xn$1,$xn$2,$xn$3,...)=$ p$($xn$|$xn$1)$for all n$.$ Show that, for a stationary Markov process, the entropy rate is given by H$($Xn$|$Xn$1).$