A1 Refereed original research article in a scientific journal
Homomorphisms preserving deterministic context-free languages
Authors: Tommi Lehtinen, Alexander Okhotin
Publication year: 2013
Journal: International Journal of Foundations of Computer Science
Journal acronym: IJFCS
Number in series: 7
Volume: 24
Issue: 7
First page : 1049
Last page: 1066
Number of pages: 18
ISSN: 0129-0541
DOI: https://doi.org/10.1142/S0129054113400303
Abstract
The paper characterizes the family of homomorphisms, under which the deterministic context-free languages, the LL context-free languages and the unambiguous context-free languages are closed. The family of deterministic context-free languages is closed under a homomorphism h if and only if h is either a code of bounded deciphering delay, or the images of all symbols under h are powers of the same string. The same characterization holds for LL context-free languages. The unambiguous context-free languages are closed under h if and only if either h is a code, or the images of all symbols under h are powers of the same string.
The paper characterizes the family of homomorphisms, under which the deterministic context-free languages, the LL context-free languages and the unambiguous context-free languages are closed. The family of deterministic context-free languages is closed under a homomorphism h if and only if h is either a code of bounded deciphering delay, or the images of all symbols under h are powers of the same string. The same characterization holds for LL context-free languages. The unambiguous context-free languages are closed under h if and only if either h is a code, or the images of all symbols under h are powers of the same string.
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