[1] NASH-WILLIAMS C. St. I. A.: Hamiltonian circuits in graphs and digraphs. The many facets of graph theory. (Proceedings of a Conference at Western Michigan University in November 1968, edited by Chartrand, G. and Kapcor, S. F), Springer - Verlag, Berlin, Heidelberg and New York, 1969, pp. 237-243. MR 0252263