Monotone deterministic RL-automata don't need auxiliary symbols

Abstract

It is known that for monotone deterministic one-way restarting automata, the use of auxiliary symbols does not increase the expressive power. Here we show that the same is true for deterministic two-way restarting automata that are right- or left-monotone. Actually in these cases it suffices to admit delete operations instead of the more general rewrite operations. In addition, we characterize the classes of languages that are accepted by these types of two-way restarting automata by certain combinations of deterministic pushdown automata and deterministic transducers. © Springer-Verlag Berlin Heidelberg 2005.