@article{MZ_1951__54_169232,
     author = {G.A. Dirac},
     title = {Note on the colouring graphs.},
     journal = {Mathematische Zeitschrift},
     pages = {347--353},
     year = {1951},
     volume = {54},
     zbl = {0043.38502},
     url = {http://geodesic.mathdoc.fr/item/MZ_1951__54_169232/}
}