Handbook of logic in computer science (vol. 3)
The Boolean Hierarchy of NP-Partitions
STACS '00 Proceedings of the 17th Annual Symposium on Theoretical Aspects of Computer Science
Undecidability in the homomorphic quasiorder of finite labeled forests
CiE'06 Proceedings of the Second conference on Computability in Europe: logical Approaches to Computational Barriers
On the Wadge Reducibility of k-Partitions
Electronic Notes in Theoretical Computer Science (ENTCS)
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We show that many so called discrete weak semilatticesconsidered earlier in a series of author's publications havehereditary undecidable first-order theories. Since such structuresappear naturally in some parts of computability theory, we obtainseveral new undecidability results. This applies e.g. to thestructures of complete numberings, of m-degrees of indexsets and of the Wadge degrees of partitions in the Baire space andω-algebraic domains.