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On restricted context-free grammars
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SYSNO ASEP 0367493 Document Type J - Journal Article R&D Document Type Journal Article Subsidiary J Článek ve WOS Title On restricted context-free grammars Author(s) Dassow, J. (DE)
Masopust, Tomáš (MU-W) RID, ORCID, SAISource Title Journal of Computer and System Sciences. - : Elsevier - ISSN 0022-0000
Roč. 78, č. 1 (2012), s. 293-304Number of pages 12 s. Language eng - English Country US - United States Keywords context-free grammars ; derivation restriction ; normal forms Subject RIV BA - General Mathematics CEZ AV0Z10190503 - MU-W (2005-2011) UT WOS 000297833200021 EID SCOPUS 81955160869 DOI 10.1016/j.jcss.2011.05.008 Annotation Context-free grammars are widely used for the simple form of their rules. A derivation step consists of the choice of a nonterminal of the sentential form and of an application of a rule rewriting it. Several regulations of the derivation process have been studied to increase the power of context-free grammars. In the resulting grammars, however, not only the symbols to be rewritten are restricted, but also the rules to be applied. In this paper, we study context-free grammars with a simpler restriction where only symbols to be rewritten are restricted, not the rules, in the sense that any rule rewriting the chosen nonterminal can be applied. We prove that these grammars have the same power as random context, matrix, or programmed grammars. We also present two improved normal forms and discuss the characterization of context-sensitive languages by a variant using strings of length at most two instead of symbols. Workplace Mathematical Institute Contact Jarmila Štruncová, struncova@math.cas.cz, library@math.cas.cz, Tel.: 222 090 757 Year of Publishing 2012
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