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Poincaré Conjecture In mathematics, the Poincaré conjecture Poincaré conjecture (/pwæ̃.kɑːˈreɪ/; French: [pwɛ̃kaʁe])[1] is a theorem about the characterization of the 3sphere, which is the hypersphere that bounds the unit ball in fourdimensional space. The conjecture states:Every simply connected, closed 3manifold 3manifold is homeomorphic to the 3sphere.An equivalent form of the conjecture involves a coarser form of equivalence than homeomorphism called homotopy equivalence: if a 3manifold 3manifold is homotopy equivalent to the 3sphere, then it is necessarily homeomorphic to it. Originally conjectured by Henri Poincaré, the theorem concerns a space that locally looks like ordinary threedimensional space but is connected, finite in size, and lacks any boundary (a closed 3manifold) [...More...]  "Poincaré Conjecture" on: Wikipedia Yahoo Parouse 

Compact Space In mathematics, and more specifically in general topology, compactness is a property that generalizes the notion of a subset of Euclidean space being closed (that is, containing all its limit points) and bounded (that is, having all its points lie within some fixed distance of each other). Examples include a closed interval, a rectangle, or a finite set of points. This notion is defined for more general topological spaces than Euclidean space Euclidean space in various ways. One such generalization is that a topological space is sequentially compact if every infinite sequence of points sampled from the space has an infinite subsequence that converges to some point of the space. The Bolzano–Weierstrass theorem Bolzano–Weierstrass theorem states that a subset of Euclidean space is compact in this sequential sense if and only if it is closed and bounded [...More...]  "Compact Space" on: Wikipedia Yahoo Parouse 

Hypersphere In geometry of higher dimensions, a hypersphere is the set of points at a constant distance from a given point called its center. It is a manifold of codimension one, i.e. with one dimension less than that of the ambient space. As the radius increases the curvature of the hypersphere decreases; in the limit a hypersphere approaches the zero curvature of a hyperplane. Hyperplanes and hyperspheres are examples of hypersurfaces. The term hypersphere was introduced by Duncan Sommerville Duncan Sommerville in his discussion of models for nonEuclidean geometry.[1] The first one mentioned is a 3sphere 3sphere in four dimensions. Some spheres are not hyperspheres: if S is a sphere in Em where m < n and the space has n dimensions, then S is not a hypersphere. Similarly, any nsphere in a proper flat is not a hypersphere [...More...]  "Hypersphere" on: Wikipedia Yahoo Parouse 

Wolfgang Haken Wolfgang Haken (born June 21, 1928 in Berlin, Germany) is a mathematician who specializes in topology, in particular 3manifolds. In 1962 he left Germany Germany to become a visiting professor at the University of Illinois at UrbanaChampaign, he became a full professor by 1965, and he is now an emeritus professor. In 1976 together with colleague Kenneth Appel, also at the University of Illinois at UrbanaChampaign, Haken solved one of the most famous problems in mathematics, the fourcolor problem. They proved that any map can be filled in with four colors without any adjacent "countries" sharing the same color. Haken has introduced several important ideas, including Haken manifolds, Kneser–Haken finiteness, and an expansion of the work of Kneser into a theory of normal surfaces. Much of his work has an algorithmic aspect, and he is one of the influential figures in algorithmic topology [...More...]  "Wolfgang Haken" on: Wikipedia Yahoo Parouse 

Fundamental Group In the mathematical field of algebraic topology, the fundamental group is a mathematical group associated to any given pointed topological space that provides a way to determine when two paths, starting and ending at a fixed base point, can be continuously deformed into each other. It records information about the basic shape, or holes, of the topological space. The fundamental group is the first and simplest homotopy group. The fundamental group is a topological invariant: homeomorphic topological spaces have the same fundamental group. Fundamental groups can be studied using the theory of covering spaces, since a fundamental group coincides with the group of deck transformations of the associated universal covering space. The abelianization of the fundamental group can be identified with the first homology group of the space [...More...]  "Fundamental Group" on: Wikipedia Yahoo Parouse 

Topological Invariant In topology and related areas of mathematics a topological property or topological invariant is a property of a topological space which is invariant under homeomorphisms. That is, a property of spaces is a topological property if whenever a space X possesses that property every space homeomorphic to X possesses that property. Informally, a topological property is a property of the space that can be expressed using open sets. A common problem in topology is to decide whether two topological spaces are homeomorphic or not [...More...]  "Topological Invariant" on: Wikipedia Yahoo Parouse 

Enrico Betti Enrico Betti Enrico Betti Glaoui (21 October 1823 – 11 August 1892) was an Italian mathematician, now remembered mostly for his 1871 paper on topology that led to the later naming after him of the Betti numbers. He worked also on the theory of equations, giving early expositions of Galois theory. He also discovered Betti's theorem, a result in the theory of elasticity.Contents1 Biography 2 Works 3 See also 4 Notes 5 Further reading 6 External linksBiography[edit] Betti was born in Pistoia, Tuscany. He graduated from the University of Pisa Pisa in 1846 under Giuseppe Doveri (it) (1792–1857).[1] In Pisa, he was also a student of Ottaviano Fabrizio Mossotti Ottaviano Fabrizio Mossotti and Carlo Matteucci. After a time teaching, he held an appointment there from 1857. In 1858 he toured Europe with Francesco Brioschi Francesco Brioschi and Felice Casorati, meeting Bernhard Riemann [...More...]  "Enrico Betti" on: Wikipedia Yahoo Parouse 

Homology (mathematics) In mathematics, homology[1] is a general way of associating a sequence of algebraic objects such as abelian groups or modules to other mathematical objects such as topological spaces. Homology groups were originally defined in algebraic topology. Similar constructions are available in a wide variety of other contexts, such as abstract algebra, groups, Lie algebras, Galois theory, and algebraic geometry. The original motivation for defining homology groups was the observation that two shapes can be distinguished by examining their holes. For instance, a circle is not a disk because the circle has a hole through it while the disk is solid, and the ordinary sphere is not a circle because the sphere encloses a twodimensional hole while the circle encloses a onedimensional hole. However, because a hole is "not there", it is not immediately obvious how to define a hole or how to distinguish different kinds of holes [...More...]  "Homology (mathematics)" on: Wikipedia Yahoo Parouse 

Sphere A sphere (from Greek σφαῖρα — sphaira, "globe, ball"[1]) is a perfectly round geometrical object in threedimensional space that is the surface of a completely round ball (viz., analogous to a circular object in two dimensions). Like a circle, which geometrically is an object in twodimensional space, a sphere is defined mathematically as the set of points that are all at the same distance r from a given point, but in threedimensional space.[2] This distance r is the radius of the ball, and the given point is the center of the mathematical ball [...More...]  "Sphere" on: Wikipedia Yahoo Parouse 

Algebraic Topology Algebraic topology Algebraic topology is a branch of mathematics that uses tools from abstract algebra to study topological spaces. The basic goal is to find algebraic invariants that classify topological spaces up to homeomorphism, though usually most classify up to homotopy equivalence. Although algebraic topology primarily uses algebra to study topological problems, using topology to solve algebraic problems is sometimes also possible [...More...]  "Algebraic Topology" on: Wikipedia Yahoo Parouse 

Combinatorial Topology In mathematics, combinatorial topology was an older name for algebraic topology, dating from the time when topological invariants of spaces (for example the Betti numbers) were regarded as derived from combinatorial decompositions of spaces, such as decomposition into simplicial complexes. After the proof of the simplicial approximation theorem this approach provided rigour. The change of name reflected the move to organise topological classes such as cyclesmoduloboundaries explicitly into abelian groups. This point of view is often attributed to Emmy Noether,[1] and so the change of title may reflect her influence. The transition is also attributed to the work of Heinz Hopf,[2] who was influenced by Noether, and to Leopold Vietoris Leopold Vietoris and Walther Mayer, who independently defined homology.[3] A fairly precise date can be supplied in the internal notes of the Bourbaki group [...More...]  "Combinatorial Topology" on: Wikipedia Yahoo Parouse 

Topology In mathematics, topology (from the Greek τόπος, place, and λόγος, study) is concerned with the properties of space that are preserved under continuous deformations, such as stretching, crumpling and bending, but not tearing or gluing. This can be studied by considering a collection of subsets, called open sets, that satisfy certain properties, turning the given set into what is known as a topological space. Important topological properties include connectedness and compactness.[1] Topology Topology developed as a field of study out of geometry and set theory, through analysis of concepts such as space, dimension, and transformation.[2] Such ideas go back to Gottfried Leibniz, who in the 17th century envisioned the geometria situs (GreekLatin for "geometry of place") and analysis situs (GreekLatin for "picking apart of place") [...More...]  "Topology" on: Wikipedia Yahoo Parouse 

Boundary (topology) In topology and mathematics in general, the boundary of a subset S of a topological space X is the set of points which can be approached both from S and from the outside of S. More precisely, it is the set of points in the closure of S not belonging to the interior of S. An element of the boundary of S is called a boundary point of S [...More...]  "Boundary (topology)" on: Wikipedia Yahoo Parouse 

Closed Manifold In mathematics, a closed manifold is a type of topological space, namely a compact manifold without boundary. In contexts where no boundary is possible, any compact manifold is a closed manifold. Compact manifolds are, in an intuitive sense, "finite". By the basic properties of compactness, a closed manifold is the disjoint union of a finite number of connected closed manifolds. One of the most basic objectives of geometric topology is to understand what the supply of possible closed manifolds is.Contents1 Examples 2 Properties 3 Contrasting terms 4 Use in physics 5 ReferencesExamples[edit] The simplest example is a circle, which is a compact onedimensional manifold. Other examples of closed manifolds are the torus and the Klein bottle. As a counterexample, the real line is not a closed manifold because it is not compact [...More...]  "Closed Manifold" on: Wikipedia Yahoo Parouse 

Unit Ball In mathematics, a unit sphere is the set of points of distance 1 from a fixed central point, where a generalized concept of distance may be used; a closed unit ball is the set of points of distance less than or equal to 1 from a fixed central point. Usually a specific point has been distinguished as the origin of the space under study and it is understood that a unit sphere or unit ball is centered at that point. Therefore one speaks of "the" unit ball or "the" unit sphere. For example, a onedimensional sphere is the surface of what is commonly called a "circle", while such a circle's interior and surface together are the twodimensional ball. Similarly, a twodimensional sphere is the surface of the Euclidean solid known colloquially as a "sphere", while the interior and surface together are the threedimensional ball. A unit sphere is simply a sphere of radius one [...More...]  "Unit Ball" on: Wikipedia Yahoo Parouse 

Path (topology) In mathematics, a path in a topological space X is a continuous function f from the unit interval I = [0,1] to Xf : I → X.The initial point of the path is f(0) and the terminal point is f(1). One often speaks of a "path from x to y" where x and y are the initial and terminal points of the path. Note that a path is not just a subset of X which "looks like" a curve, it also includes a parameterization. For example, the maps f(x) = x and g(x) = x2 represent two different paths from 0 to 1 on the real line. A loop in a space X based at x ∈ X is a path from x to x. A loop may be equally well regarded as a map f : I → X with f(0) = f(1) or as a continuous map from the unit circle S1 to Xf : S1 → X.This is because S1 may be regarded as a quotient of I under the identification 0 ∼ 1. The set of all loops in X forms a space called the loop space of X. A topological space for which there exists a path connecting any two points is said to be pathconnected [...More...]  "Path (topology)" on: Wikipedia Yahoo Parouse 