Copyright © 2002 Elsevier Science B.V. All rights reserved.
Converting two-way nondeterministic unary automata into simpler automata
Received 22 August 2001;
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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
states.
Author Keywords: Formal languages; Finite state automata; Unary languages






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