@article{10_4153_CJM_1973_043_3,
     author = {Tutte, W. T.},
     title = {Chromatic {Sums} for {Rooted} {Planar} {Triangulations:} {The} {Cases} \ensuremath{\lambda} = 1 and \ensuremath{\lambda} = 2},
     journal = {Canadian journal of mathematics},
     pages = {426--447},
     year = {1973},
     volume = {25},
     number = {2},
     doi = {10.4153/CJM-1973-043-3},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1973-043-3/}
}