📝 SummarXiv

Abstract

A $d$-limited automaton is a Turing machine that may rewrite each input cell at most~$d$ times. Hibbard (1967) showed that for every $d \geq 2$ such automata recognize all context-free languages and that deterministic $d$-limited automata form a strict hierarchy. Later, Pighizzini and Pisoni proved that the second level of this hierarchy coincides with deterministic context-free languages (DCFLs). We present a linear-time recognition algorithm for deterministic $d$-limited automata in the RAM model, thereby extending linear-time recognition beyond DCFLs. We further generalize this result to deterministic $d(n)$-limited automata, where the bound $d$ may depend on the input length $n$. In addition, we prove an $O(n \cdot k \cdot d(n) + m)$ bound for the membership problem, where the input includes both the word and the automaton's description, with $m$ denoting the size of the description and $k$ the number of states.