1. W. Hamilton, Tour around the world: Twenty towns on the earth are figured by the 20 vertices of a regular dodecahedron (a polyhedron with 12 pentagonal faces and 20 vertices).
2. C. Berge,Graphes et hypergraphes (Dunod, Paris, 1970).
3. L. Euler,Commentationes Arithmeticae Collectae (St. Peterburg, 1766), p. 337.
4. P. W. Kasteleyn,Physica 29:1329 (1963).
5. F. Harary, ed.,Graph Theory and Theoretical Physics (Academic Press, London, 1967).