“…From this point of view, we first proposed four-dimensional automata as computational models of four-dimensional pattern processing in 2002, and investigated their several accepting powers [21]. Since then, we have introduced several four-dimensional automata, and investigated their accepting powers and recognizability [22,24,26,27,32]. On the other hand, the classes of sets recognized by two-or three-dimensional probabilistic finite automata and probabilistic Turing machines have been studied extensively [3-6, 9, 12-15, 17-19, 25, 28, 29, 33-35].…”