@article{JRAM_1964__0214_0215_150603,
     author = {G.A. Dirac},
     title = {On the structure of 5- and 6-chromatic abstract graphs.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {43--52},
     publisher = {mathdoc},
     volume = {0214_0215},
     year = {1964},
     zbl = {0131.38403},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1964__0214_0215_150603/}
}