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It was shown by \textit{W. Thomas} [Trees in algebra and programming, 9th Coll., Bordeaux, France, 31-49 (1984; Zbl 0557.68051)] that for tree languages the notions of first-order definability, aperiodicity and star- freeness are not equivalent as they are in the case of regular word languages. He also gave some relationships between the corresponding families of tree languages. The picture of the situation is complemented by proving that the first-order definable tree languages form a proper subfamily of the aperiodic regular tree languages, and by showing how the first-order definable tree languages can be obtained as a subfamily of the star-free tree languages. Methods based on Ehrenfeucht-Fraissé games are used for both results.
Formal languages and automata, tree languages, first-order definability, Automata and formal grammars in connection with logical questions, tree automata
Formal languages and automata, tree languages, first-order definability, Automata and formal grammars in connection with logical questions, tree automata
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impulse This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network. | Average |