The Power of One-State Turing Machines

Abstract

At first glance, one-state Turing machines are very weak: the halting problem for them is decidable, and, without memory, they cannot even accept a simple one element language such as $L = \{ 1 \}$ . Nevertheless it has been showed that a one-state Turing machine can accept non regular languages. We extend such result and prove that they can also recognize non context-free languages, so for some tasks they are more powerful than pushdown automata.