Nonterminal separation in graph grammars

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Abstract

The notion of nonterminal separation in eNCE graph grammars is introduced: such a graph grammar is k-separated (with k⩾1) if the distance between any two nonterminal nodes in any of its sentential forms is at least k (2-separated eNCE grammars are known as boundary eNCE graph grammars). There exists a 2-separated eNCE graph language that is not 3-separated. Apex eNCE graph grammars can be arbitrarily separated: every apex eNCE graph language can be generated by a k-separated apex eNCE grammar, for every k.

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The work of this author was conducted as part of the PRISMA project, a joint effort with Philips Research, partially supported by the Dutch “Stimuleringsprojectteam informaticaonderzoek” (SPIN).