Stack versus sensitivity for one-way automata

Abstract

We consider one-way multihead automata recognizing 2-bounded languages, i.e., languages L such that L ⊆ 1 ∗2 ∗ . We compare computational power of a stack and sensitivity, that is, capability of recognizing whether the heads stand at the same place. We show that each 2-bounded language recognized by a nonsensing multihead one-way deterministic pushdown automaton (1-DPDA) can be recognized by a sensing 3-head one-way deterministic finite automaton. So, the stack plus any number of heads counts less than sensitivity plus only 3 heads. Also, we present a simple characterization of the 2-bounded languages recognized by 1-DPDA.