1. L. D. Landau and E. M. Lifshitz, Course of Theoretical Physics, Vol. 1: Mechanics (Fizmatlit, Moscow, 2004; Pergamon, Oxford, 1976).
2. E. Cartan, Geometry of Riemannian Spaces (Math Sci., Brookline, 1983).
3. J. H. Mason, Math. Gaz. 56, 194 (1972).
4. G. Ringel, Map Color Theorem (Mir, Moscow, 1977) [in Russian].
5. H. S. M. Coxeter, Regular Polytopes (Dover, New York, 1973).