Three-way automata on rectangular tapes over a one-letter alphabet
Information Sciences: an International Journal
Two-dimensional finite state recognizability
Fundamenta Informaticae - Special issue on formal language theory
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Regular Expressions and Context-Free Grammars for Picture Languages
STACS '97 Proceedings of the 14th Annual Symposium on Theoretical Aspects of Computer Science
New Results on Alternating and Non-deterministic Two-Dimensional Finite-State Automata
STACS '01 Proceedings of the 18th Annual Symposium on Theoretical Aspects of Computer Science
New operations and regular expressions for two-dimensional languages over one-letter alphabet
Theoretical Computer Science - The art of theory
Automata on a 2-dimensional tape
FOCS '67 Proceedings of the 8th Annual Symposium on Switching and Automata Theory (SWAT 1967)
DLT'03 Proceedings of the 7th international conference on Developments in language theory
Regular expressions for two-dimensional languages over one-letter alphabet
DLT'04 Proceedings of the 8th international conference on Developments in Language Theory
Picture Languages: From Wang Tiles to 2D Grammars
CAI '09 Proceedings of the 3rd International Conference on Algebraic Informatics
A computational model for tiling recognizable two-dimensional languages
Theoretical Computer Science
Tiling automaton: a computational model for recognizable two-dimensional languages
CIAA'07 Proceedings of the 12th international conference on Implementation and application of automata
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The aim of this paper is to investigate sequential models to describe two-dimensional languages. The intent is to add more capabilities to 4NFA in order to encompass a wider class of languages. We show that any (tiling) recognizable language can be simulated by a 4NFA with an extra queue whose size is bounded by the minimum of the two dimensions of a picture; and that 2NFA (i.e. automata moving only in two directions) with an analogous queue are sufficient when the alphabet is unary. A special class of recognizable languages can be simulated also by 4-way pushdown automata with a stack of size bounded by the sum of the two dimensions of the picture. Such a class is also characterized by a recursive definition involving the operations of union, intersection and a new diagonal overlapping operation applied to languages recognized by 2NFA.