1. Arnol?d, V.I. (1983). Geometrical Methods in the Theory of Ordinary Differential Equations. Springer-Verlag.
2. Ball, P. (1999). The Self-Made Tapestry. Oxford University Press.
3. Christaller, W. (1933). Die zentralen Orte in Süddeutschland. Jena.
4. Coxeter, H.S.M. (1969). Introduction to Geometry. John Wiley & Sons, Inc.
5. Henle, M. (1979). A Combinatorial Introduction to Topology. Freeman.