Abstract
We study the nature of the generating series of some models of walks with small steps in the three quarter plane. More precisely, we restrict ourselves to the situation where the group is infinite, the kernel has genus one, and the step set is diagonally symmetric (i.e., with no steps in anti-diagonal directions). In that situation, after a transformation of the plane, we derive a quadrant-like functional equation. Among the four models of walks, we obtain, using difference Galois theory, that three of them have a differentially transcendental generating series, and one has a differentially algebraic generating series.
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Notes
Thereafter, the expressions avoiding a quadrant, confined to the three quadrants, and confined to the three quarter plane, will be used with no distinction.
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Acknowledgements
The authors want to warmly thank the referees for their detailed and helpful comments. The authors also thank Samuel Simon for his help with the English language, Kilian Raschel, and Manuel Kauers, for their suggestions.
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Communicated by Marni Mishna.
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This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme under the Grant Agreement No. 759702. This project has received funding from the ANR de rerum natura ANR-19-CE40-0018. A. Trotignon was supported by the Austrian Science Fund (FWF) grant FWF05004.
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Dreyfus, T., Trotignon, A. On the Nature of Four Models of Symmetric Walks Avoiding a Quadrant. Ann. Comb. 25, 617–644 (2021). https://doi.org/10.1007/s00026-021-00541-8
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DOI: https://doi.org/10.1007/s00026-021-00541-8