1. On the order of uniquely (k, m)-colourable graphs;Broere;Discrete Math,1990
2. A generalization of the chromatic number;Chartrand,1968
3. Graphs and Digraphs;Chartrand,1986
4. A problem in graph theory;Erdős;Amer. Math. Monthly,1964
5. A survey of (m, k)-colourings;Frick,1991