A topological space is a set endowed with a structure, called a Topology, which allows defining continuous deformation of subspaces, and, more generally, all kinds of Continuity. Euclidean Space, and, more generally, Metric Space are examples of topological spaces, as any distance or metric defines a topology. The deformations that are considered in topology are Homeomorphism and Homotopy. A property that is invariant under such deformations is a “topological property”. The following are basic examples of topological properties: