English

A construction for a counterexample to the pseudo 2-factor isomorphic graph conjecture

Combinatorics 2022-07-25 v1

Abstract

A graph GG admiting a 22-factor is \textit{pseudo 22-factor isomorphic} if the parity of the number of cycles in all its 22-factors is the same. In [M. Abreu, A.A. Diwan, B. Jackson, D. Labbate and J. Sheehan. Pseudo 22-factor isomorphic regular bipartite graphs. Journal of Combinatorial Theory, Series B, 98(2) (2008), 432-444.] some of the authors of this note gave a partial characterisation of pseudo 22-factor isomorphic bipartite cubic graphs and conjectured that K3,3K_{3,3}, the Heawood graph and the Pappus graph are the only essentially 44-edge-connected ones. In [J. Goedgebeur. A counterexample to the pseudo 22-factor isomorphic graph conjecture. Discr. Applied Math., 193 (2015), 57-60.] Jan Goedgebeur computationally found a graph G\mathscr{G} on 3030 vertices which is pseudo 22-factor isomorphic cubic and bipartite, essentially 44-edge-connected and cyclically 66-edge-connected, thus refuting the above conjecture. In this note, we describe how such a graph can be constructed from the Heawood graph and the generalised Petersen graph GP(8,3)GP(8,3), which are the Levi graphs of the Fano 737_3 configuration and the M\"obius-Kantor 838_3 configuration, respectively. Such a description of G\mathscr{G} allows us to understand its automorphism group, which has order 144144, using both a geometrical and a graph theoretical approach simultaneously. Moreover we illustrate the uniqueness of this graph.

Keywords

Cite

@article{arxiv.2207.10961,
  title  = {A construction for a counterexample to the pseudo 2-factor isomorphic graph conjecture},
  author = {M. Abreu and M. Funk and D. Labbate and F. Romaniello},
  journal= {arXiv preprint arXiv:2207.10961},
  year   = {2022}
}
R2 v1 2026-06-25T01:08:28.990Z