Displaying similar documents to “The helping hierarchy”

On the expressive power of the shuffle operator matched with intersection by regular sets

Joanna Jȩdrzejowicz, Andrzej Szepietowski (2001)

RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications

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We investigate the complexity of languages described by some expressions containing shuffle operator and intersection. We show that deciding whether the shuffle of two words has a nonempty intersection with a regular set (or fulfills some regular pattern) is NL-complete. Furthermore we show that the class of languages of the form L ∩ R , with a shuffle language L and a regular language R , contains non-semilinear languages and does not form a family of mildly context- sensitive languages. ...

Equality sets for recursively enumerable languages

Vesa Halava, Tero Harju, Hendrik Jan Hoogeboom, Michel Latteux (2005)

RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications

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We consider shifted equality sets of the form E G ( a , g 1 , g 2 ) = { w ∣ g 1 ( w ) = a g 2 ( w ) } , where g 1 and g 2 are nonerasing morphisms and a is a letter. We are interested in the family consisting of the languages h ( E G ( J ) ) , where h is a coding and E G ( J ) is a shifted equality set. We prove several closure properties for this family. Moreover, we show that every recursively enumerable language L ⊆ A * is a projection of a shifted equality set, that is, L = π A ( E G ( a , g 1 , g 2 ) ) for some (nonerasing) morphisms g 1 and g 2 and a letter a , where π A deletes the letters not in A . Then...

Self-reproducing pushdown transducers

Alexander Meduna, Luboš Lorenc (2005)

Kybernetika

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After a translation of an input string, x , to an output string, y , a self- reproducing pushdown transducer can make a self-reproducing step during which it moves y to its input tape and translates it again. In this self- reproducing way, it can repeat the translation n -times for any n ≥ 1 . This paper demonstrates that every recursively enumerable language can be characterized by the domain of the translation obtained from a self- reproducing pushdown transducer that repeats its translation...

Efficiency of automata in semi-commutation verification techniques

Gérard Cécé, Pierre-Cyrille Héam, Yann Mainier (2008)

RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications

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Computing the image of a regular language by the transitive closure of a relation is a central question in regular model checking. In a recent paper Bouajjani et al. [IEEE Comput. Soc. (2001) 399–408] proved that the class of regular languages L – called APC – of the form ∪ j L 0 , j L 1 , j L 2 , j ... L k j , j , where the union is finite and each L i , j is either a single symbol or a language of the form B * with B a subset of the alphabet, is...