ALGEBRAIC CHARACTERIZATION OF LOGICALLY DEFINED TREE LANGUAGES
Abstract
We give an algebraic characterization of the tree languages that are defined by logical formulas using certain Lindström quantifiers. An important instance of our result concerns first-order definable tree languages. Our characterization relies on the usage of preclones, an algebraic structure introduced by the authors in a previous paper, and of the block product operation on preclones. Our results generalize analogous results on finite word languages, but it must be noted that, as they stand, they do not yield an algorithm to decide whether a given regular tree language is first-order definable.
This paper was prepared while the first author was affiliated with Rovira i Virgili University, Tarragona, Spain. The first author acknowledges partial support from grant MTM2007 63422 from the Ministry of Education and Science of Spain. The second author acknowledges partial support from the French ANR (projet DOTS) and the Indo-French project TIMED DISCOVERI. Both authors acknowledge support from the European Science Foundation program AUTOMATHA and from CNRS-HAS.
Dedicated to the Memory of Bret Tilson