Paper

Endmarkers can make a difference

Abstract

We show that the nonemptiness problem for two-way automata with only one endmarker over unary alphabets is complete for nondeterministic logarithmic space. This should be contrasted with the corresponding problem for two-way automata with two endmarkers, which is known to be NP-complete. © 1990.

M.J. Slattery, Joan L. Mitchell

IBM J. Res. Dev