Given a subset S of ℕ, filtering a word α0α1 ⋯ αn by S consists in deleting the letters αi such that i is not in S. By a natural generalization, denote by L[S], where L is a language, the set of all words of L filtered by S. The filtering problem is to characterize the filters S such that, for every recognizable language L, L[S] is recognizable. In this paper, the filtering problem is solved, and a unified approach is provided to solve similar questions, including the removal problem considered by Seiferas and McNaughton. There are two main ingredients on our approach: the first one is the notion of residually ultimately periodic sequences, and the second one is the notion of representable transductions. © Springer-Verlag Berlin Heidelberg 2003.
CITATION STYLE
Berstel, J., Boasson, L., Carton, O., Petazzoni, B., & Pin, J. É. (2003). Operations preserving recognizable languages. Lecture Notes in Computer Science (Including Subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 2751, 343–354. https://doi.org/10.1007/978-3-540-45077-1_32
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