Almeida, Jorge and Klima, Ondrej - New decidable upper bound of the second level in the Straubing-Therien concatenation hierarchy of star-free languages

dmtcs:490 - Discrete Mathematics & Theoretical Computer Science, January 1, 2010, Vol. 12 no. 4
New decidable upper bound of the second level in the Straubing-Therien concatenation hierarchy of star-free languages

Authors: Almeida, Jorge and Klima, Ondrej

In a recent paper we gave a counterexample to a longstanding conjecture concerning the characterization of regular languages of level 2 in the Straubing-Therien concatenation hierarchy of star-free languages. In that paper a new upper bound for the corresponding pseudovariety of monoids was implicitly given. In this paper we show that it is decidable whether a given monoid belongs to the new upper bound. We also prove that this new upper bound is incomparable with the previous upper bound.


Source : oai:HAL:hal-00990443v1
Volume: Vol. 12 no. 4
Published on: January 1, 2010
Submitted on: March 26, 2015
Keywords: formal languages,regular languages,concatenation hierarchies,level two,star-free languages,[INFO.INFO-DM] Computer Science [cs]/Discrete Mathematics [cs.DM]


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