Decision Problems For Convex Languages
Abstract
In this paper we examine decision problems associated with various classes of convex languages, studied by Ang and Brzozowski (under the name "continuous languages"). We show that we can decide whether a given language L is prefix-, suffix-, factor-, or subword-convex in polynomial time if L is represented by a DFA, but that the problem is PSPACE-hard if L is represented by an NFA. In the case that a regular language is not convex, we prove tight upper bounds on the length of the shortest words demonstrating this fact, in terms of the number of states of an accepting DFA. Similar results are proved for some subclasses of convex languages: the prefix-, suffix-, factor-, and subword-closed languages, and the prefix-, suffix-, factor-, and subword-free languages.
Keywords
Cite
@article{arxiv.0808.1928,
title = {Decision Problems For Convex Languages},
author = {Janusz Brzozowski and Jeffrey Shallit and Zhi Xu},
journal= {arXiv preprint arXiv:0808.1928},
year = {2009}
}
Comments
preliminary version. This version corrected one typo in Section 2.1.1, line 4