@article{10_4153_CMB_1966_016_x,
     author = {Bowen, Robert},
     title = {On {Sums} of {Valencies} in {Planar} {Graphs}},
     journal = {Canadian mathematical bulletin},
     pages = {111--114},
     year = {1966},
     volume = {9},
     number = {1},
     doi = {10.4153/CMB-1966-016-x},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1966-016-x/}
}