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Theoretical Computer Science
Volume 295, Issues 1-3, 24 February 2003, Pages 189-203
 
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doi:10.1016/S0304-3975(02)00403-6    How to Cite or Link Using DOI (Opens New Window)
Copyright © 2002 Elsevier Science B.V. All rights reserved.

Converting two-way nondeterministic unary automata into simpler automata

Viliam GeffertE-mail The Corresponding Author, a, 1, Carlo MereghettiE-mail The Corresponding Author, b and Giovanni PighizziniCorresponding Author Contact Information, E-mail The Corresponding Author, c

a Department of Computer Science, P.J. Image afárik University, Jesenná 5, 04154, KoImage ice, Slovakia b Dipartimento di Informatica, Sistemistica e Comunicazione, Università degli Studi di Milano, Bicocca, via Bicocca degli Arcimboldi 8, 20126, Milano, Italy c Dipartimento di Scienze dell'Informazione, Università degli Studi di Milano, via Comelico 39, I-20135, Milano, Italy

Received 22 August 2001; 
revised 29 October 2001; 
accepted 8 January 2002. ;
Available online 6 January 2003.

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Abstract

We show that, on inputs of length exceeding 5n2, any n-state unary two-way nondeterministic finite automaton (2nfa) can be simulated by a (2n+2)-state quasi-sweeping 2nfa. Such a result, besides providing a “normal form” for 2nfa's, enables us to get a subexponential simulation of unary 2nfa's by two-way deterministic finite automata (2dfa's). In fact, we prove that any n-state unary 2nfa can be simulated by a sweeping 2dfa with Image states.

Author Keywords: Formal languages; Finite state automata; Unary languages


Theoretical Computer Science
Volume 295, Issues 1-3, 24 February 2003, Pages 189-203
 
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