A computer-assisted proof of Barnette-Goodey conjecture: Not only fullerene graphs are Hamiltonian. Frantiˇsek Kardoˇs LaBRI, University of Bordeaux, France
[email protected] August 18, 2017 Abstract Fullerene graphs, i.e., 3-connected planar cubic graphs with pentagonal and hexag- onal faces, are conjectured to be Hamiltonian. This is a special case of a conjecture of Barnette and Goodey, stating that 3-connected planar graphs with faces of size at most 6 are Hamiltonian. We prove the conjecture. 1 Introduction Tait conjectured in 1880 that cubic polyhedral graphs (i.e., 3-connected planar cubic graphs) are Hamiltonian. The first counterexample to Tait’s conjecture was found by Tutte in 1946; later many others were found, see Figure 1. Had the conjecture been true, it would have implied the Four-Color Theorem. However, each known non-Hamiltonian cubic polyhedral graph has at least one face of size 7 or more [1, 17]. It was conjectured that all cubic polyhedral graphs with maximum face size at most 6 are Hamiltonian. In the literature, the conjecture is usually attributed to Barnette (see, e.g., [13]), however, Goodey [6] stated it in an informal way as well. This conjecture covers in particular the class of fullerene graphs, 3-connected cubic planar graphs with pentagonal and hexagonal faces only. Hamiltonicity was verified for all fullerene graphs with up to 176 vertices [1]. Later on, the conjecture in the general form was verified arXiv:1409.2440v2 [math.CO] 16 Aug 2017 for all graphs with up to 316 vertices [2]. On the other hand, cubic polyhedral graphs having only faces of sizes 3 and 6 or 4 and 6 are known to be Hamiltonian [6, 7].