Counterexamples to Negami's Conjecture have ply at least 14

Dickson Y. B. Annor, Yuri Nikolayevsky, Michael S. Payne

Published 2023-11-03Version 1

S. Negami conjectured in $1988$ that a connected graph has a finite planar cover if and only if it embeds in the projective plane. It follows from the works of D. Archdeacon, M. Fellows, P. Hlin\v{e}n\'{y}, and S. Negami that the conjecture is true if the graph $K_{2, 2, 2, 1}$ has no finite planar cover. We prove that $K_{2, 2, 2, 1}$ has no planar cover of ply less than $14$ and consequently, any counterexample to Negami's conjecture has ply at least 14 and at least $98$ vertices.