1. C. Berge, The Theory of Graphs and Its Application [Russian translation], IL, 1962.
2. C. E. Shannon, “A theorem on the coloring of the rays of a graph,” Cybernetics Collection [Russian translation], I, IL, 249–253, 1960, (see also C. Shannon, Studies in Information Theory and Cybernetics [Russian translation], IL, 735 739, 1963.
3. D. König, Theorie der endlichen und unendlichen Graphen, Leipzig, 1936.
4. C. Berge, “Les problèmes de coloration en théorie des graphes,” Publs. Inst. Statist. Univ. Paris, 9, no. 2, 123–160, 1960.
5. O. Ore, Theory of Graphs, American Mathematical Society, Providence, R. I., 1962.