1. W. W. Rouse Ball and H. S. M. Coxeter, Mathematical Recreations and Essays, Macmillan, New York, 1947.
2. C. Berge, The Theory of Graphs and its Application, Dunod, Paris, 1958 (in French); Methuen, London, 1962 (in English).
3. Six-Rings in Minimal Five-Color Maps
4. Another Reducible Edge Configuration