A subdivision of a closed surface X is a finite collection of vertices and edges in X such that (i) every edge begins and ends in a vertex, (ii) edges intersect in vertices, (iii) the complement of the vertices and edges has connected components which are homeomorphic to an open disc; these are known as faces. The Euler characteristic of X the surface then equals V–E+F, where V, E, F denotes the number of vertices, edges, and faces respectively. See triangulation.