Unambiguous recognizable two-dimensional languages

@article{Anselmo2006UnambiguousRT,
  title={Unambiguous recognizable two-dimensional languages},
  author={Marcella Anselmo and Dora Giammarresi and Maria Madonia and Antonio Restivo},
  journal={RAIRO Theor. Informatics Appl.},
  year={2006},
  volume={40},
  pages={277-293}
}
We consider the family UREC of unambiguous recognizable two-dimensional languages. We prove that there are recognizable languages that are inherently ambiguous, that is UREC family is a proper subclass of REC family. The result is obtained by showing a necessary condition for unambiguous recognizable languages. Further UREC family coincides with the class of picture languages defined by unambiguous 2OTA and it strictly contains its deterministic counterpart. Some closure and non-closure… 

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Deterministic and unambiguous two-dimensional languages over one-letter alphabet

...

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