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Locality Testing for NFAs is PSPACE-complete

Published: November 10, 2025 | arXiv ID: 2511.07361v1

By: Antoine Amarilli, Mikaël Monet, Rémi De Pretto

Potential Business Impact:

Checks if a computer program is "local" fast.

Business Areas:
Natural Language Processing Artificial Intelligence, Data and Analytics, Software

The class of local languages is a well-known subclass of the regular languages that admits many equivalent characterizations. In this short note we establish the PSPACE-completeness of the problem of determining, given as input a nondeterministic finite automaton (NFA) A, whether the language recognized by A is local or not. This contrasts with the case of deterministic finite automata (DFA), for which the problem is known to be in PTIME.

Page Count
3 pages

Category
Computer Science:
Formal Languages and Automata Theory