Separating k-separated eNCE graph languages

Changwook Kim, Dong Hoon Lee

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


An eNCE graph grammar is k-separated (k≥1) if the distance between any two nonterminal nodes in any of its sentential forms is at least k. Let SEPk denote the class of graph languages generated by k-separated grammars. Then, SEP1 (SEP2) is the class of eNCE (boundary eNCE) graph languages, and so SEP2{subset of with not equal to}SEP1. Recently, Engelfriet (1991) showed that SEP3{subset of with not equal to}SEP2 and conjectured that, in fact, SEPk+1{subset of with not equal to}SEPk for each k≥ 1. We prove this conjecture affirmatively.

Original languageEnglish
Pages (from-to)247-259
Number of pages13
JournalTheoretical Computer Science
Issue number2
Publication statusPublished - 1993 Nov 22
Externally publishedYes

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Computer Science(all)


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