1. L. W.Beineke and R. J.Wilson, On the edge-chromatic number of a graph. To appear in Discrete Mathematics.
2. C.Berge, Theorie des graphes et ses applications. Paris 1958.
3. C.Berge, Graphes et hypergraphes. Paris 1970.
4. G. A. Dirac, On the structure of 5- and 6-chromatic abstract graphs. J. reine angew. Math.214/215, 43?52 (1964).
5. G. Haj�s, �ber eine Konstruktion nichtn-f�rbbarer Graphen. Wiss. Z. Martin Luther Univ., Halle-Wittenberg A10, 116?117 (1961).