Information Processing Letters
An NP-complete language accepted in linear time by a one-tape Turing machine
Theoretical Computer Science
Worm-2DPDAs: an extension to 2DPDAs that can be simulated in linear time
Information Processing Letters
Complexity results for two-way and multi-pebble automata and their logics
ICALP '94 Selected papers from the 21st international colloquium on Automata, languages and programming
“Maximal-munch” tokenization in linear time
ACM Transactions on Programming Languages and Systems (TOPLAS)
Characterizations of Pushdown Machines in Terms of Time-Bounded Computers
Journal of the ACM (JACM)
A Linear-Time On-Line Recognition Algorithm for ``Palstar''
Journal of the ACM (JACM)
Computers and Intractability: A Guide to the Theory of NP-Completeness
Computers and Intractability: A Guide to the Theory of NP-Completeness
Generalizing Cook's Transformation to Imperative Stack Programs
Proceedings of the Colloquium in Honor of Arto Salomaa on Results and Trends in Theoretical Computer Science
Collage of two-dimensional words
Theoretical Computer Science - The art of theory
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The basic finite automata model has been extended over the years with different acceptance modes (nondeterminism, alternation), new or improved devices (two-way heads, pebbles, nested pebbles) and with cooperation. None of these additions permits recognition of non-regular languages. The purpose of this work is to investigate a new kind of automata which is inspired by an extension of 2DPDAs. Mogensen enhanced these with what he called a WORM (write once, read many) track and showed that Cook's linear-time simulation result still holds. Here we trade the pushdown store for nondeterminism or a pebble and show that the languages of these new types of finite automata are still regular. The conjunction of alternation, or of nondeterminism and a pebble permits the recognition of non-regular languages. We give examples of languages that are easy to recognize and of operations that are easy to perform using these WORM tracks under nondeterminism. While somewhat similar to Hennie machines, our models do not require an explicit time bound on their computations.