Epsilon-reducible context-free languages and characterizations of indexed languages
نویسندگان
چکیده
منابع مشابه
Permutations of context-free and indexed languages
We consider the cyclic closure of a language, and its gener-alisation to the operators C k introduced by Brandstädt. We prove that the cyclic closure of an indexed language is indexed, and that if L is a context-free language then C k (L) is indexed.
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In this article, we provide three coalgebraic characterizations of the class of context-free languages, each based on the idea of adding coalgebraic structure to an existing algebraic structure by specifying output-derivative pairs. Final coalgebra semantics then gives an interpretation function into the final coalgebra of all languages with the usual output and derivative operations. The first...
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Indexed languages are languages recognized by pushdown automata of level 2 and by indexed grammars. We propose here some new characterizations linking indexed languages to context-free languages: the class of indexed languages is the image of the Dyck language by a nice class of context-free transducers, it is also the class of images, by a projection defined by an FO-formula of nested words la...
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For a language L, we consider its cyclic closure, and more generally the language C(L), which consists of all words obtained by partitioning words from L into k factors and permuting them. We prove that the classes of ET0L and EDT0L languages are closed under the operators C. This both sharpens and generalises Brandstädt’s result that if L is context-free then C(L) is context-sensitive and not ...
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We give “syntactic” characterizations of context-sensitive languages (CSLs) in terms of some restricted models of symport/antiport P systems. These are the first such characterizations of CSLs in terms of P systems. In particular, we show the following for any language L over a binary alphabet: 1. Let m be any integer ≥ 1. Then L is a CSL if and only if it can be accepted by a restricted sympor...
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ژورنال
عنوان ژورنال: Information and Computation
سال: 2019
ISSN: 0890-5401
DOI: 10.1016/j.ic.2019.104444