Unambiguous recognizable two-dimensional languages

Marcella Anselmo, Dora Giammarresi, Maria Madonia, Antonio Restivo
2006 RAIRO - Theoretical Informatics and Applications  
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
more » ... es of UREC are presented. Finally we show that it is undecidable whether a given tiling system is unambiguous.
doi:10.1051/ita:2006008 fatcat:6ad3fsdvzfesbeanox4kenvwny