[1] Bharucha-Reid A. T.: Elements of the Theory of Markov Processes and their Applications. New York, J. Willey and Sons, 1960. MR 0112177 | Zbl 0095.32803
[2] Ore O.: Theory of graphs. American Mathematical Society, Rhode Island, 1962. MR 0150753 | Zbl 0105.35401