Bouttier, J.; Di Francesco, P.; Guitter, E «Geodesic distance in planar graphs». Nuclear Physics B, 663, 3, 7-2003, pàg. 535–567. DOI: 10.1016/S0550-3213(03)00355-9. «By distance we mean here geodesic distance along the graph, namely the length of any shortest path between say two given faces»
