New decidable upper bound of the second level in the Straubing-Thérien concatenation hierarchy of star-free languages
| Authors | |
|---|---|
| Year of publication | 2010 |
| Type | Article in Periodical |
| Magazine / Source | Discrete Mathematics & Theoretical Computer Science |
| MU Faculty or unit | |
| Citation | |
| Field | General mathematics |
| Keywords | formal languages; regular languages; concatenation hierarchies; level two; star-free languages |
| Description | In a recent paper we gave a counterexample to a longstanding conjecture concerning the characterization of regular languages of level 2 in the Straubing-Thérien 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. |
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