Abstract
A regular unranked tree folding consists of a regular unranked tree language and a folding operation that merges, i.e., folds, selected nodes of a tree to form a graph; the combination is a formal device for representing graph languages. If, in the process of folding, the order among edges is discarded so that the result is an unordered graph, then two applications of a fold operation is enough to make the associated parsing problem NP-complete. However, if the order is kept, then the problem is solvable in non-uniform polynomial time. In this paper we address the remaining case where only one fold operation is applied, but the order among edges is discarded. We show that under these conditions, the problem is solvable in non-uniform polynomial time.
J. Björklund—Supported by the Swedish Research Council under Grant Number 2020-03852, and by the Wallenberg AI, Autonomous Systems and Software Program through the NEST project STING.
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We would like to express our sincere gratitude to the anonymous reviewers for their constructive feedback, which greatly improved the quality of this manuscript.
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Berglund, M., Björklund, H., Björklund, J. (2023). Parsing Unranked Tree Languages, Folded Once. In: Fernau, H., Jansen, K. (eds) Fundamentals of Computation Theory. FCT 2023. Lecture Notes in Computer Science, vol 14292. Springer, Cham. https://doi.org/10.1007/978-3-031-43587-4_5
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