Abstract
We consider the question of whether or not a given primitive substitution preserves its sets of return words—or return sets for short. More precisely, we study the property asking that the image of the return set to a word equals the return set to the image of that word. We show that, for bifix encodings (where images of letters form a bifix code), this property holds for all but finitely many words. On the other hand, we also show that every conjugacy class of Sturmian substitutions contains a member for which the property fails infinitely often. Various applications and examples of these results are presented, including a description of the subgroups generated by the return sets in the shift of the Thue–Morse substitution. Up to conjugacy, these subgroups can be sorted into strictly decreasing chains of isomorphic subgroups weaving together a simple pattern. This is in stark contrast with the Sturmian case, and more generally with the dendric case (including in particular the Arnoux–Rauzy case), where it is known that all return sets generate the free group over the underlying alphabet.
This work was supported by the Agence Nationale de la Recherche through the project “Codys” (ANR-18-CE40-0007).
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References
Almeida, J.: Profinite groups associated with weakly primitive substitutions. J. Math. Sci. 144(2), 3881–3903 (2007). https://doi.org/10.1007/s10958-007-0242-y, translated from Fundam. Prikl. Mat., 11(3), 13–48 (2005)
Almeida, J., Costa, A.: Presentations of Schützenberger groups of minimal subshifts. Israel J. Math. 196(1), 1–31 (2013). https://doi.org/10.1007/s11856-012-0139-4
Almeida, J., Costa, A.: A geometric interpretation of the Schützenberger group of a minimal subshift. Ark. Math. 54(2), 243–275 (2016). https://doi.org/10.1007/s11512-016-0233-7
Balková, L., Pelantová, E., Steiner, W.: Sequences with constant number of return words. Monatsh. Math. 155(3–4), 251–263 (2008). https://doi.org/10.1007/s00605-008-0001-2
Berstel, J., Séébold, P.: A remark on morphic Sturmian words. RAIRO - Theor. Inform. Appl. 28(3–4), 255–263 (1994). https://doi.org/10.1051/ita/1994283-402551
Berstel, J., De Felice, C., Perrin, D., Reutenauer, C., Rindone, G.: Bifix codes and Sturmian words. J. Algebra 369, 146–202 (2012). https://doi.org/10.1016/j.jalgebra.2012.07.013
Berstel, J., Perrin, D., Reutenauer, C.: Codes and Automata. Cambridge University Press (2009). https://doi.org/10.1017/cbo9781139195768
Berstel, J., Séébold, P.: A characterization of Sturmian morphisms. In: Borzyszkowski, A., Sokołowski, S. (eds.) Lecture Notes in Computer Science, vol. 711, pp. 281–290. Springer, Berlin Heidelberg (1993). https://doi.org/10.1007/3-540-57182-5_20
Berthé, V., Dolce, F., Durand, F., Leroy, J., Perrin, D.: Rigidity and substitutive dendric words. Int. J. Found. Comput. 29(05), 705–720 (2018). https://doi.org/10.1142/S0129054118420017
Berthé, V., et al.: Acyclic, connected and tree sets. Monatsh. Math. 176(4), 521–550 (2015). https://doi.org/10.1007/s00605-014-0721-4
Berthé, V., et al.: Maximal bifix decoding. Discrete Math. 338(5), 725–742 (2015). https://doi.org/10.1016/j.disc.2014.12.010
Costa, A.: Conjugacy invariants of subshifts: An approach from profinite semigroup theory. Int. J. Algebra Comput. 16(4), 629–655 (2006). https://doi.org/10.1142/s0218196706003232
Durand, F.: A generalization of Cobham’s theorem. Theoret. Comput. Sci. 31(2), 169–185 (1998). https://doi.org/10.1007/s002240000084
Durand, F.: A characterization of substitutive sequences using return words. Discrete Math. 179(1–3), 89–101 (1998). https://doi.org/10.1016/S0012-365X(97)00029-0
Durand, F., Host, B., Skau, C.: Substitutional dynamical systems, Bratteli diagrams and dimension groups. Ergod. Theory Dyn. Syst. 19(4), 953–993 (1999). https://doi.org/10.1017/S0143385799133947
Durand, F., Leroy, J.: The constant of recognizability is computable for primitive morphisms. J. Integer S. 20 (2017)
Durand, F., Perrin, D.: Dimension Groups and Dynamical Systems. Cambridge Studies in Advanced Mathematics, Cambridge University Press (2022). https://doi.org/10.1017/9781108976039
Goulet-Ouellet, H.: Pronilpotent quotients associated with primitive substitutions. J. Algebra 606, 341–370 (2022). https://doi.org/10.1016/j.jalgebra.2022.05.021
Goulet-Ouellet, H.: Suffix-connected languages. Theoret. Comput. Sci. 923, 126–143 (2022). https://doi.org/10.1016/j.tcs.2022.05.001
Kapovich, I., Myasnikov, A.: Stallings foldings and subgroups of free groups. J. Algebra 248(2), 608–668 (2002). https://doi.org/10.1006/jabr.2001.9033
Klouda, K.: Bispecial factors in circular non-pushy D0L languages. Theoret. Comput. Sci. 445, 63–74 (2012). https://doi.org/10.1016/j.tcs.2012.05.007
Kyriakoglou, R.: Iterated morphisms, combinatorics on words and symbolic dynamical systems. Ph.D. thesis, Université Paris-Est (2019)
Lothaire, M.: Algebraic combinatorics on words, Encyclopedia of Mathematics and its Applications, vol. 90. Cambridge University Press, Cambridge (2002). https://doi.org/10.1017/CBO9781107326019
de Luca, A., Mione, L.: On bispecial factors of the Thue-Morse word. Inf. Process. Lett. 49(4), 179–183 (1994). https://doi.org/10.1016/0020-0190(94)90008-6
Lyndon, R.C., Schupp, P.E.: Combinatorial Group Theory. Springer, Berlin Heidelberg (2001). https://doi.org/10.1007/978-3-642-61896-3
Mignosi, F., Séébold, P.: Morphismes sturmiens et règles de Rauzy. J. Théor. Nr. Bordx. 5(2), 221–233 (1993). https://doi.org/10.5802/jtnb.91
Mossé, B.: Puissance de mots et reconnaissabilité des points fixes d’une substitution. Theoret. Comput. Sci. 99(2), 327–334 (1992). https://doi.org/10.1016/0304-3975(92)90357-L
Queffélec, M.: Substitution dynamical systems–spectral analysis, Lecture Notes in Mathematics, vol. 1294. Springer-Verlag, Berlin, second edn. (2010). https://doi.org/10.1007/978-3-642-11212-6
Séébold, P.: On the conjugation of standard morphisms. Theoret. Comput. Sci. 195(1), 91–109 (1998). https://doi.org/10.1016/s0304-3975(97)00159-x
Touikan, N.W.M.: A fast algorithm for Stallings’ folding process. Int. J. Algebra Comput. 16(6), 1031–1045 (2006). https://doi.org/10.1142/S0218196706003396
Vuillon, L.: A characterization of Sturmian words by return words. Europ. J. Comb. 22(2), 263–275 (2001). https://doi.org/10.1006/eujc.2000.0444
Wen, Z.X., Wen, Z.Y.: Local isomorphisms of the invertible substitutions. C. R. Acad. Sci. Paris 318, 299–304 (1994)
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Berthé, V., Goulet-Ouellet, H. (2023). On Substitutions Preserving Their Return Sets. In: Frid, A., Mercaş, R. (eds) Combinatorics on Words. WORDS 2023. Lecture Notes in Computer Science, vol 13899. Springer, Cham. https://doi.org/10.1007/978-3-031-33180-0_6
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