“…But here we would like to mention the class of processes known in the literature as a Persistent random walk (PRW), a Goldstein-Kac random walk, or also a correlated random walk, see [9] for definitions and short historical introduction. The increments of these random walks are not independent but form a Markov chain and are closely related to the chains with unbounded variable length memory, see [9,10]. These random walks can be considered as a chain with unbounded variable length memory with the special context tree on the binary alphabet called by the authors as a double (infinite) comb context tree [9].…”