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MFCS

2001

Springer

2001

Springer

Abstract. We prove that the class of context-free languages with polynomially bounded ambiguity (PCFL) is the closure of the class of unambiguous languages (UCFL) under projections which deletes Parikh bounded symbols only. A symbol a is Parikh bounded in a language L if there is a constant c such that no word of L contains more than c occurrences of a. Furthermore PCFL is closed under the formally stronger operation of Parikh bounded substitution, i.e., a substitution which is the identity for non Parikh bounded symbols. Finally we prove that the closure of UCFL under union and concatenation is a proper subset of PCFL.

Related Content

Added |
30 Jul 2010 |

Updated |
30 Jul 2010 |

Type |
Conference |

Year |
2001 |

Where |
MFCS |

Authors |
Klaus Wich |

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