Search results for " context-free languages"

showing 3 items of 3 documents

On block pumpable languages

2016

Ehrenfeucht, Parikh and Rozenberg gave an interesting characterisation of the regular languages called the block pumping property. When requiring this property only with respect to members of the language but not with respect to nonmembers, one gets the notion of block pumpable languages. It is shown that these block pumpable are a more general concept than regular languages and that they are an interesting notion of their own: they are closed under intersection, union and homomorphism by transducers; they admit multiple pumping; they have either polynomial or exponential growth.

Discrete mathematicsGeneral Computer ScienceAbstract family of languagesComputer Science::Computation and Language (Computational Linguistics and Natural Language and Speech Processing)0102 computer and information sciences02 engineering and technology01 natural sciencesCone (formal languages)Pumping lemma for regular languagesTheoretical Computer ScienceCombinatoricsRegular languageIntersection010201 computation theory & mathematicsBlock (programming)0202 electrical engineering electronic engineering information engineering020201 artificial intelligence & image processingHomomorphismPumping lemma for context-free languagesComputer Science::Formal Languages and Automata TheoryMathematicsTheoretical Computer Science
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Cancellation, pumping and permutation in formal languages

1984

Formal grammarTheoretical computer scienceChomsky hierarchyFormal languageContext-free languageAbstract family of languagesPumping lemma for context-free languagesArithmeticCone (formal languages)Pumping lemma for regular languagesMathematics
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On Prefix Normal Words

2011

We present a new class of binary words: the prefix normal words. They are defined by the property that for any given length $k$, no factor of length $k$ has more $a$'s than the prefix of the same length. These words arise in the context of indexing for jumbled pattern matching (a.k.a. permutation matching or Parikh vector matching), where the aim is to decide whether a string has a factor with a given multiplicity of characters, i.e., with a given Parikh vector. Using prefix normal words, we give the first non-trivial characterization of binary words having the same set of Parikh vectors of factors. We prove that the language of prefix normal words is not context-free and is strictly contai…

permutation matchingcontext-free languagesSearch engine indexingpre-necklacesBinary numberParikh vectorsComputer Science::Computation and Language (Computational Linguistics and Natural Language and Speech Processing)Lyndon wordsnon- standard pattern matchingLyndon wordsCombinatoricsPrefixjumbled pattern matchingPattern matchingParikh vectors; pre-necklaces; Lyndon words; context-free languages; jumbled pattern matching; permutation matching; non- standard pattern matching; indexingComputer Science::Formal Languages and Automata TheoryParikh vectors pre-necklaces Lyndon words context-free languages jumbled pattern matching permutation matching non-standard pattern matching indexingMathematicsindexing
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