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Counterexamples to “A conjecture on induced subgraphs of Cayley graphs”. (English) Zbl 1465.05195

Summary: Recently, H. Huang [Ann. Math. (2) 190, No. 3, 949–955 (2019; Zbl 1427.05116)] gave a very elegant proof of the Sensitivity Conjecture by proving that hypercube graphs have the following property: every induced subgraph on a set of more than half the vertices has maximum degree at least \(\sqrt{d}\), where \(d\) is the valency of the hypercube. This was generalised by N. Alon and K. Zheng [Adv. Comb. 2020, Paper No. 11, 12 p. (2020; Zbl 1455.05022)] who proved that every Cayley graph on an elementary abelian 2-group has the same property. Very recently, A. Potechin and H. Y. Tsang [“A conjecture on induced subgraphs of Cayley graphs”, Preprint, arXiv:2003.13166] proved an analogous results for Cayley graphs on abelian groups. They also conjectured that all Cayley graphs have the analogous property. We disprove this conjecture by constructing various counterexamples, including an infinite family of Cayley graphs of unbounded valency which admit an induced subgraph of maximum valency 1 on a set of more than half the vertices.

MSC:

05E18 Group actions on combinatorial structures
05C25 Graphs and abstract algebra (groups, rings, fields, etc.)

References:

[1] N. Alon and K. Zheng, Unitary signings and induced subgraphs of Cayley graphs ofZn2, arXiv:2003.04926[math.CO].
[2] F. R. K. Chung, Z. F¨uredi, R. L. Graham and P. Seymour, On induced subgraphs of the cube,J. Comb. Theory Ser. A49(1988), 180-187, doi:10.1016/0097-3165(88)90034-9. · Zbl 0653.05037
[3] I.Garc´ıa-MarcoandK.Knauer,OnsensitivityinbipartiteCayleygraphs, arXiv:2009.00554[math.CO].
[4] C. D. Godsil, More odd graph theory,Discrete Math.32(1980), 205-207, doi:10.1016/ 0012-365x(80)90055-2. · Zbl 0438.05053
[5] H. Huang, Induced subgraphs of hypercubes and a proof of the sensitivity conjecture,Ann. of Math.190(2019), 949-955, doi:10.4007/annals.2019.190.3.6. · Zbl 1427.05116
[6] N. Nisan and M. Szegedy, On the degree of Boolean functions as real polynomials,Comput. Complex.4(1994), 301-313, doi:10.1007/bf01263419. · Zbl 0829.68047
[7] A.
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