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Let $L_{>\lambda}(\mathcal{A})$ and $L_{\geq\lambda}(\mathcal{A})$ be the languages recognized by {\em measure many 1-way quantum finite automata (MM-QFA)} (or,{\em enhanced 1-way quantum finite automata(EQFA)}) $\mathcal{A}$ with strict…

Formal Languages and Automata Theory · Computer Science 2023-06-06 Tianrong Lin

It is an open problem to characterize the class of languages recognized by quantum finite automata (QFA). We examine some necessary and some sufficient conditions for a (regular) language to be recognizable by a QFA. For a subclass of…

Quantum Physics · Physics 2007-05-23 Andris Ambainis , Arnolds Kikusts , Maris Valdats

In automata theory, while determinisation provides a standard route to solving many common problems in automata theory, some weak forms of nondeterminism can be dealt with in some problems without costly determinisation. For example, the…

Formal Languages and Automata Theory · Computer Science 2026-05-29 Thomas A. Henzinger , Keya Prakash , K. S. Thejaswini

We discuss the problem of learning a deterministic finite automaton (DFA) from a confidence oracle. That is, we are given access to an oracle $Q$ with incomplete knowledge of some target language $L$ over an alphabet $\Sigma$; the oracle…

Formal Languages and Automata Theory · Computer Science 2023-11-21 Wilson Wu

In the present work, we lay out a new theory showing that all automata can always be co-lexicographically partially ordered, and an intrinsic measure of their complexity can be defined and effectively determined, namely, the minimum width…

Formal Languages and Automata Theory · Computer Science 2023-05-04 Nicola Cotumaccio , Giovanna D'Agostino , Alberto Policriti , Nicola Prezza

We introduce and study the repetitive variants of the deterministic and the nondeterministic finite automaton with translucent words (DFAwtw and NFAwtw). On seeing the right sentinel, a repetitive NFAwtw need not halt immediately, accepting…

Formal Languages and Automata Theory · Computer Science 2025-07-22 František Mráz , Friedrich Otto

The state complexity, respectively, nondeterministic state complexity of a regular language $L$ is the number of states of the minimal deterministic, respectively, of a minimal nondeterministic finite automaton for $L$. Some of the most…

Formal Languages and Automata Theory · Computer Science 2026-04-08 Arto Salomaa , Kai Salomaa , Taylor J. Smith

Given a nondeterministic finite-state automaton (NFA), we aim to estimate the size of an equivalent deterministic finite-state automaton (DFA). We demonstrate that computing the state complexity of an NFA within polynomial precision is…

Formal Languages and Automata Theory · Computer Science 2025-10-20 Ivan Baburin , Ryan Cotterell

We investigate the descriptional complexity of different variants of 1-limited automata (1-las), an extension of two-way finite automata (2nfas) characterizing regular languages. In particular, we consider 2nfas with common-guess…

Formal Languages and Automata Theory · Computer Science 2025-05-01 Bruno Guillon , Luca Prigioniero , Javad Taheri

We generalize some of the central results in automata theory to the abstraction level of coalgebras and thus lay out the foundations of a universal theory of automata operating on infinite objects. Let F be any set functor that preserves…

Logic in Computer Science · Computer Science 2015-07-01 C. Kupke , Y. Venema

Consider the finite regular language L_n = {w0 : w \in {0,1}^*, |w| \le n}. It was shown by Ambainis, Nayak, Ta-Shma and Vazirani that while this language is accepted by a deterministic finite automaton of size O(n), any one-way quantum…

Quantum Physics · Physics 2007-05-23 Ashwin Nayak

We show that for any two distinct words $ s_1, s_2 $ over an arbitrary alphabets, there exists a deterministic finite automaton with $ O(\log^2 n) $ states that accepts $ s_1 $ and rejects $ s_2 $. This improves the previous upper bound of…

Formal Languages and Automata Theory · Computer Science 2025-04-03 Bogdan C. Dumitru

We focus on the family of $(k,l)$-unambiguous automata that encompasses the one of deterministic $k$-lookahead automata introduced by Han and Wood. We show that this family presents nice theoretical properties that allow us to compute…

Formal Languages and Automata Theory · Computer Science 2017-05-12 Pascal Caron , Marianne Flouret , Ludovic Mignot

We introduce a quantum-like classical computational model, called affine computation, as a generalization of probabilistic computation. After giving the basics of affine computation, we define affine finite automata (AfA) and compare it…

Formal Languages and Automata Theory · Computer Science 2016-06-07 Alejandro Díaz-Caro , Abuzer Yakaryılmaz

#NFA refers to the problem of counting the words of length $n$ accepted by a non-deterministic finite automaton. #NFA is #P-hard, and although fully-polynomial-time randomized approximation schemes (FPRAS) exist, they are all impractical.…

Data Structures and Algorithms · Computer Science 2025-07-01 Kuldeep S. Meel , Alexis de Colnet

This paper presents and analyzes an incremental algorithm for the construction of Acyclic Non-deterministic Finite-state Automata (NFA). Automata of this type are quite useful in computational linguistics, especially for storing lexicons.…

Data Structures and Algorithms · Computer Science 2007-05-23 Kyriakos N. Sgarbas , Nikos D. Fakotakis , George K. Kokkinakis

Counter automata are more powerful versions of finite-state automata where addition and subtraction operations are permitted on a set of n integer registers, called counters. We show that the word problem of $\Z^n$ is accepted by a…

Group Theory · Mathematics 2007-05-23 Sean Cleary , Murray Elder , Gretchen Ostheimer

Determining the minimum number of states required by a finite automaton to separate a given pair of different words is an important problem. In this paper, we consider this problem for quantum automata (QFAs). We show that 2-state QFAs can…

Formal Languages and Automata Theory · Computer Science 2016-02-26 Aleksandrs Belovs , Juan Andres Montoya , Abuzer Yakaryılmaz

A Wheeler automaton is a finite state automaton whose states admit a total Wheeler order, reflecting the co-lexicographic order of the strings labeling source-to-node paths. A Wheeler language is a regular language admitting an accepting…

Formal Languages and Automata Theory · Computer Science 2023-12-19 Ruben Becker , Davide Cenzato , Sung-Hwan Kim , Bojana Kodric , Alberto Policriti , Nicola Prezza

This paper deals with the size complexity of minimal {\it two-way quantum finite automata} (2qfa's) necessary for operations to perform on all inputs of each fixed length. Such a complexity measure, known as state complexity of operations,…

Discrete Mathematics · Computer Science 2008-07-04 Daowen Qiu