Unambiguous recognizable two-dimensional languages
Marcella Anselmo, Dora Giammarresi, Maria Madonia, Antonio Restivo (2006)
RAIRO - Theoretical Informatics and Applications
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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...