@article{10_4153_CMB_1972_063_2,
     author = {Cockayne, E. J.},
     title = {Colour {Classes} for {r-Graphs}},
     journal = {Canadian mathematical bulletin},
     pages = {349--354},
     year = {1972},
     volume = {15},
     number = {3},
     doi = {10.4153/CMB-1972-063-2},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1972-063-2/}
}