Example image of eyePlorer eyePlorer map for 'Euler characteristic': Algebraic topology Mathematics Polyhedral combinatorics Topological property Topological space Chi (letter) Greek alphabet Platonic solid Polyhedron Leonhard Euler Homology (mathematics) Edge (geometry) Face (geometry) Vertex (geometry) Planar graph Stereographic projection Augustin-Louis Cauchy David Eppstein Imre Lakatos Proofs and Refutations CW complex Simplicial complex Betti number Rank of an abelian group Singular homology Group isomorphism Homotopy Inclusion-exclusion principle Interior (topology) Compact space Locally compact space Support (mathematics) Topologically stratified space Algebraic variety Complex number Complement (set theory) Counterexample Product topology Real line Subset Cardinality Set (mathematics) Covering space Ramification Riemann–Hurwitz formula Fibration Connected space Serre spectral sequence Closed manifold Poincaré duality