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In this paper, we present a proof of the NP-completeness of computing the smallest Deterministic Finite Automaton (DFA) that distinguishes two given regular languages as DFAs. A distinguishing DFA is an automaton that recognizes a language…

Formal Languages and Automata Theory · Computer Science 2023-06-07 Jan Martens

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…

Formal Languages and Automata Theory · Computer Science 2025-11-11 Antoine Amarilli , Mikaël Monet , Rémi De Pretto

We observe that the classical Cartesian product construction for the intersection of (languages of) nondeterministic finite automata (NFA) is non-optimal in the worst case, if the automata have many transitions. For a fixed alphabet, the…

Formal Languages and Automata Theory · Computer Science 2026-05-21 Dmitry Chistikov , Neha Rino

Families of deterministic finite automata (FDFA) represent regular $\omega$-languages through their ultimately periodic words (UP-words). An FDFA accepts pairs of words, where the first component corresponds to a prefix of the UP-word, and…

Formal Languages and Automata Theory · Computer Science 2025-06-17 León Bohn , Yong Li , Christof Löding , Sven Schewe

The problem DFA-Intersection-Nonemptiness asks if a given number of deterministic automata accept a common word. In general, this problem is PSPACE-complete. Here, we investigate this problem for the subclasses of commutative automata and…

Formal Languages and Automata Theory · Computer Science 2021-08-12 Henning Fernau , Stefan Hoffmann , Michael Wehar

We reinvestigate known lower bounds for the Intersection Non-Emptiness Problem for Deterministic Finite Automata (DFA's). We first strengthen conditional time complexity lower bounds from T. Kasai and S. Iwata (1985) which showed that…

Formal Languages and Automata Theory · Computer Science 2026-03-24 Michael Wehar

Affine finite automata (AfA) can be more succinct than probabilistic and quantum finite automata when recognizing some regular languages with bounded-error. In this paper, we improve previously known constructions given for the succinctness…

Formal Languages and Automata Theory · Computer Science 2021-07-01 Abuzer Yakaryılmaz

History-deterministic automata are those in which nondeterministic choices can be correctly resolved stepwise: there is a strategy to select a continuation of a run given the next input letter so that if the overall input word admits some…

Formal Languages and Automata Theory · Computer Science 2026-04-01 Soumyajit Paul , David Purser , Sven Schewe , Qiyi Tang , Patrick Totzke , Di-De Yen

We introduce deterministic suffix-reading automata (DSA), a new automaton model over finite words. Transitions in a DSA are labeled with words. From a state, a DSA triggers an outgoing transition on seeing a word ending with the…

Formal Languages and Automata Theory · Computer Science 2026-05-13 R Keerthan , B Srivathsan , R Venkatesh , Sagar Verma

We present a language $L_n$ which is recognizable by a probabilistic finite automaton (PFA) with probability $1 - \epsilon$ for all $\epsilon > 0$ with $O(log^2n)$ states, with a deterministic finite automaton (DFA) with O(n) states, but a…

Quantum Physics · Physics 2007-05-23 Gatis Midrijanis

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

We introduce deterministic suffix-reading automata (DSA), a new automaton model over finite words. Transitions in a DSA are labeled with words. From a state, a DSA triggers an outgoing transition on seeing a word ending with the…

Formal Languages and Automata Theory · Computer Science 2024-10-31 R Keerthan , B Srivathsan , R Venkatesh , Sagar Verma

This paper establishes a lower bound on the number of states necessary in the worst case to simulate an $n$-state two-way nondeterministic finite automaton (2NFA) by a one-way unambiguous finite automaton (UFA). It is proved that for every…

Formal Languages and Automata Theory · Computer Science 2024-12-10 Semyon Petrov , Alexander Okhotin

Algorithms which learn environments represented by automata in the past have had complexity scaling with the number of states in the automaton, which can be exponentially large even for automata recognizing regular expressions with a small…

Formal Languages and Automata Theory · Computer Science 2024-05-13 Ali Cataltepe , Vanessa Kosoy

We study the computational and descriptional complexity of the following transformation: Given a one-counter automaton (OCA) A, construct a nondeterministic finite automaton (NFA) B that recognizes an abstraction of the language L(A): its…

Formal Languages and Automata Theory · Computer Science 2016-02-11 Mohamed Faouzi Atig , Dmitry Chistikov , Piotr Hofman , K Narayan Kumar , Prakash Saivasan , Georg Zetzsche

We consider the computability and complexity of decision questions for Probabilistic Finite Automata (PFA) with sub-exponential ambiguity. We show that the emptiness problem for strict and non-strict cut-points of polynomially ambiguous…

Formal Languages and Automata Theory · Computer Science 2020-07-30 Paul C. Bell

Many natural language processing systems operate over tokenizations of text to address the open-vocabulary problem. In this paper, we give and analyze an algorithm for the efficient construction of deterministic finite automata (DFA)…

Formal Languages and Automata Theory · Computer Science 2025-05-27 Martin Berglund , Willeke Martens , Brink van der Merwe

An automaton is partially ordered if the only cycles in its transition diagram are self-loops. The expressivity of partially ordered NFAs (poNFAs) can be characterized by the Straubing-Th\'erien hierarchy. Level 3/2 is recognized by poNFAs,…

Formal Languages and Automata Theory · Computer Science 2017-04-27 Tomáš Masopust , Markus Krötzsch

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

In this paper, we consider the transition complexity of regular languages based on the incomplete deterministic finite automata. A number of results on Boolean operations have been obtained. It is shown that the transition complexity…

Formal Languages and Automata Theory · Computer Science 2010-08-11 Yuan Gao , Kai Salomaa , Sheng Yu