Subshifts are sets of colorings of ℤ^d defined by families of forbidden patterns. Given a subshift and a finite pattern, its extender set is the set of admissible completions of this pattern. It has been conjectured that the behavior of extender sets, and in particular their growth called extender entropy [French and Pavlov, 2019], could provide a way to separate the classes of sofic and effective subshifts. We prove here that both classes have the same possible extender entropies: exactly the Π₃ real numbers of [0,+∞).
@InProceedings{callard_et_al:LIPIcs.STACS.2025.21, author = {Callard, Antonin and Paviet Salomon, L\'{e}o and Vanier, Pascal}, title = {{Computability of Extender Sets in Multidimensional Subshifts}}, booktitle = {42nd International Symposium on Theoretical Aspects of Computer Science (STACS 2025)}, pages = {21:1--21:19}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-365-2}, ISSN = {1868-8969}, year = {2025}, volume = {327}, editor = {Beyersdorff, Olaf and Pilipczuk, Micha{\l} and Pimentel, Elaine and Thắng, Nguy\~{ê}n Kim}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2025.21}, URN = {urn:nbn:de:0030-drops-228462}, doi = {10.4230/LIPIcs.STACS.2025.21}, annote = {Keywords: Symbolic dynamics, subshifts, extender sets, extender entropy, computability, sofic shifts, tilings} }
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