Abstract
For fixed positive integers n and k, the Kneser graph \(KG_{n,k}\) has vertices labeled by k-element subsets of \(\{1,2,\dots ,n\}\) and edges between disjoint sets. Keeping k fixed and allowing n to grow, one obtains a family of nested graphs, each of which is acted on by a symmetric group in a way which is compatible with these inclusions and the inclusions of each symmetric group into the next. In this paper, we provide a framework for studying families of this kind using the \({{\,\mathrm{FI}\,}}\)-module theory of Church et al. (Duke Math J 164(9):1833–1910, 2015), and show that this theory has a variety of asymptotic consequences for such families of graphs. These consequences span a range of topics including enumeration, concerning counting occurrences of subgraphs, topology, concerning Hom-complexes and configuration spaces of the graphs, and algebra, concerning the changing behaviors in the graph spectra.
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Acknowledgements
We would like to send our deepest thanks to Tom Church, Andrew Snowden, and David Speyer for their helpful suggestions. We also thank Jordan Ellenberg, and John Wiltshire-Gordon for their early inspiration. Finally, we would like to thank the anonymous referee, whose thorough reading of the work improved its quality substantially.
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E. Ramos was supported by NSF Grant DMS-1704811.
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Ramos, E., White, G. Families of nested graphs with compatible symmetric-group actions. Sel. Math. New Ser. 25, 70 (2019). https://doi.org/10.1007/s00029-019-0520-9
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DOI: https://doi.org/10.1007/s00029-019-0520-9