Abstract
In this article we start a systematic study of the bi-Lipschitz geometry of lamplighter graphs. We prove that lamplighter graphs over trees bi-Lipschitzly embed into Hamming cubes with distortion at most 6. It follows that lamplighter graphs over countable trees bi-Lipschitzly embed into \(\ell _1\). We study the metric behaviour of the operation of taking the lamplighter graph over the vertex-coalescence of two graphs. Based on this analysis, we provide metric characterisations of superreflexivity in terms of lamplighter graphs over star graphs or rose graphs. Finally, we show that the presence of a clique in a graph implies the presence of a Hamming cube in the lamplighter graph over it. An application is a characterisation, in terms of a sequence of graphs with uniformly bounded degree, of the notion of trivial Bourgain–Milman–Wolfson type for arbitrary metric spaces, similar to Ostrovskii’s characterisation previously obtained in Ostrovskii (C. R. Acad. Bulgare Sci. 64(6), 775–784 (2011)).
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We thank the referees for their careful reading and the many suggestions that helped improve the exposition and clarity of the paper.
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F. Baudier was supported by the National Science Foundation under Grant Number DMS-1800322. P. Motakis was supported by National Science Foundation under Grant Numbers DMS-1600600 and DMS-1912897. Th. Schlumprecht was supported by the National Science Foundation under Grant Numbers DMS-1464713 and DMS-1711076. A. Zsák was supported by the 2018 Workshop in Analysis and Probability at Texas A&M University.
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Baudier, F., Motakis, P., Schlumprecht, T. et al. On the Bi-Lipschitz Geometry of Lamplighter Graphs. Discrete Comput Geom 66, 203–235 (2021). https://doi.org/10.1007/s00454-020-00184-1
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DOI: https://doi.org/10.1007/s00454-020-00184-1