Displaying similar documents to “Hierarchies of aperiodic languages”

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...

Classes of two-dimensional languages and recognizability conditions

Marcella Anselmo, Maria Madonia (2011)

RAIRO - Theoretical Informatics and Applications

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The paper deals with some classes of two-dimensional recognizable languages of “high complexity”, in a sense specified in the paper and motivated by some necessary conditions holding for recognizable and unambiguous languages. For such classes we can solve some open questions related to unambiguity, finite ambiguity and complementation. Then we reformulate a necessary condition for recognizability stated by Matz, introducing a new complexity function. We solve an open question proposed...

On Varieties of Literally Idempotent Languages

Ondřej Klíma, Libor Polák (2008)

RAIRO - Theoretical Informatics and Applications

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A language is literally idempotent in case that if and only if , for each , . Varieties of literally idempotent languages result naturally by taking all literally idempotent languages in a classical (positive) variety or by considering a certain closure operator on classes of languages. We initiate the systematic study of such varieties. Various classes of literally idempotent languages can be characterized using syntactic methods. A starting example is the class of all finite unions...