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The term surface used without qualification refers to surfaces without boundary. In particular, a surface with empty boundary is a surface in the usual sense. A surface with empty boundary which is compact is known as a 'closed' surface. The two-dimensional sphere, the two-dimensional torus, and the real projective plane are examples of closed ...
Appendices include additional material on embeddings and self-intersecting mappings of surfaces into three-dimensional space such as the Roman surface, the structure of finitely generated abelian groups, general topology, the history of the classification theorem, and the Hauptvermutung (the theorem that every surface can be triangulated). [2]
Absolutely closed See H-closed Accessible See . Accumulation point See limit point. Alexandrov topology The topology of a space X is an Alexandrov topology (or is finitely generated) if arbitrary intersections of open sets in X are open, or equivalently, if arbitrary unions of closed sets are closed, or, again equivalently, if the open sets are the upper sets of a poset.
A three-dimensional model of a figure-eight knot.The figure-eight knot is a prime knot and has an Alexander–Briggs notation of 4 1.. Topology (from the Greek words τόπος, 'place, location', and λόγος, 'study') is the branch of mathematics concerned with the properties of a geometric object that are preserved under continuous deformations, such as stretching, twisting, crumpling ...
In mathematics, topology is a branch of geometry concerned with the study of topological spaces. The term topology is also used for a set of open sets used to define topological spaces. See the topology glossary for common terms and their definition. Properties of general topological spaces (as opposed to manifolds) are discussed in general ...
Classical models [52] are given by the plane sections of a quadratic surface in real projective -space; if is a sphere, the geometry is called a Möbius plane. [39] The plane sections of a ruled surface (one-sheeted hyperboloid) yield the classical Minkowski plane , cf. [ 53 ] for generalizations.
The boundary of the pretzel is a genus three surface; Embedded/Immersed in Euclidean space Cross-cap; Boy's surface; Roman surface; Steiner surface; Alexander horned sphere; Klein bottle; Mapping class group. Dehn twist; Nielsen–Thurston classification
In mathematics, the surface subgroup conjecture of Friedhelm Waldhausen states that the fundamental group of every closed, irreducible 3-manifold with infinite fundamental group has a surface subgroup. By "surface subgroup" we mean the fundamental group of a closed surface not the 2-sphere.