A common cover of graphs and 2-cell embeddings.

Bojan Mohar A common cover of graphs and 2-cell embeddings. 94-106 1986 40 J. Comb. Theory, Ser. B 1 http://dx.doi.org/10.1016/0095-8956(86)90067-5 db/journals/jct/jctb40.html#Mohar86