Regular Article
Tight Lower Bounds on the Size of Sweeping Automata

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Abstract

A sweeping automaton is a two-way deterministic finite automaton which makes turns only at the endmarkers. We say that a sweeping automaton is degenerate if the automaton has no left-moving transitions. We show that for each positive integer n, there is a nondeterministic finite automaton An over a two-letter alphabet such that An has n states, whereas the smallest equivalent nondegenerate sweeping automaton has 2n states.

Keywords

deterministic finite automata
nondeterministic finite automata
two-way finite automata
sweeping automata
descriptional complexity

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This work was done during a visit of the Department of Computer Science, University of Hong Kong, supported by RGC Research Grant HKU 439/94E.