An undecidable property of context-free linear orders

Authors:
Z. íSik
Affiliations:
Department of Informatics, University of Szeged, Szeged, Hungary
Venue:
Information Processing Letters
Year:
2011

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Abstract

We prove that there exists no algorithm to decide whether the language generated by a context-free grammar is dense with respect to the lexicographic ordering. As a corollary to this result, we show that it is undecidable whether the lexicographic orderings of the languages generated by two context-free grammars have the same order type.