Resolve unresolved good common covers

Determine whether the derived graphs associated with two finite connected voltage graphs are isomorphic when every good common cover in the product graph has at least one non-regular projection covering.

Background

For two voltage graphs, the paper searches for a good common cover in the product of their underlying graphs. When the projection maps from the common cover are regular, the authors can lift and condense the voltage assignments and reduce the isomorphism question to a comparison of the resulting voltage groups.

A good common cover is called unresolved when at least one projection is not regular. The paper states that if all available good common covers are unresolved, its method cannot determine whether the two derived graphs are isomorphic.