Another approach to Planar Cover Conjecture focusing on rotation systems

We shall propose a new proof scheme for Planar Cover Conjecture, focusing on the rotation systems of planar coverings of connected graphs. We shall introduce the notion of “rotation compatible coverings” and show that a rotation compatible covering of $G$ embedded on the sphere can be covered by a regular covering of $G$ embedded on an orientable closed surface on which its covering transformation group acts. The surface may not be homeomorphic to the sphere in general, but its quotient becomes either the sphere or the projective plane which contains $G$. As an application of our theory, we shall prove that if a 3-connected graph $G$ has a 3-connected finite planar covering such that the pre-images of each vertex has sufficiently large distance, then $G$ can be embedded on the projective plane.