Regular realizability problems and context-free languages

TL;DR

This paper studies regular realizability problems with context-free filters, exploring their complexity, including P-complete, NL, and potentially intermediate cases, to understand the computational difficulty of these verification tasks.

Contribution

It introduces the analysis of RR problems with context-free filters, providing complexity classifications and discussing potential intermediate complexity cases.

Findings

Examples of P-complete RR problems

Examples of RR problems in NL

Discussion of intermediate complexity cases

Abstract

We investigate regular realizability (RR) problems, which are the problems of verifying whether intersection of a regular language -- the input of the problem -- and fixed language called filter is non-empty. In this paper we focus on the case of context-free filters. Algorithmic complexity of the RR problem is a very coarse measure of context-free languages complexity. This characteristic is compatible with rational dominance. We present examples of P-complete RR problems as well as examples of RR problems in the class NL. Also we discuss RR problems with context-free filters that might have intermediate complexity. Possible candidates are the languages with polynomially bounded rational indices.