Core Concepts
The paper proves the universality of regular realizability problems for several classes of finite relations on the set of non-negative integers, where the relations are described in a specific format. The universality is shown up to reductions using NP-oracles.
Abstract
The paper studies the regular realizability problems, which are a class of algorithmic problems parametrized by languages (called filters). An instance of the problem is a regular language described by a finite automaton, and the task is to verify the non-emptiness of the intersection between the regular language and the filter.
The main results are:
Universality of the regular realizability problems for several classes of finite relations on the set of non-negative integers. The relations are described in a format proposed by P. Wolf and H. Fernau, which allows for arbitrary order and repetitions in the list of relation elements.
The universality is shown up to reductions using NP-oracles. This corresponds to the previous results of P. Wolf and H. Fernau about the decidability of regular realizability problems for many graph-theoretic properties.
To achieve the universality results, the paper introduces a new model of Boolean function computation, which generalizes the size of decision trees and branching programs. This model is used to analyze the regular realizability problems for relation descriptions.
The paper also separately analyzes the case of relations that are invariant under bijections of the non-negative integers, as this is relevant for graph-theoretic properties that are invariant under isomorphisms.
The key technical tools used in the proofs are efficient asymptotically good codes and a framework for representing families of finite sets by directed graphs.