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Dense set information


In topology and related areas of mathematics, a subset A of a topological space X is said to be dense in X if every point of X either belongs to A or else is arbitrarily "close" to a member of A — for instance, the rational numbers are a dense subset of the real numbers because every real number either is a rational number or has a rational number arbitrarily close to it (see Diophantine approximation). Formally, is dense in if the smallest closed subset of containing is itself.[1]

The density of a topological space is the least cardinality of a dense subset of

  1. ^ Steen, L. A.; Seebach, J. A. (1995), Counterexamples in Topology, Dover, ISBN 0-486-68735-X

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Dense set

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showing that dense sets need not contain any non-empty open set. The intersection of two dense open subsets of a topological space is again dense and open...

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Nowhere dense set

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topological space is called nowhere dense or rare if its closure has empty interior. In a very loose sense, it is a set whose elements are not tightly clustered...

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Meagre set

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X} will be a topological space. The definition of meagre set uses the notion of a nowhere dense subset of X , {\displaystyle X,} that is, a subset of X...

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Baire space

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Every denseset in a Baire space is a Baire space. The result need not hold if the Gδ set is not dense. See the Examples section. Every comeagre set in...

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Mandelbrot set

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the Mandelbrot set. For example, Shishikura proved that, for a dense set of parameters in the boundary of the Mandelbrot set, the Julia set has Hausdorff...

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Julia set

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{\displaystyle \operatorname {J} (f)} is a nowhere dense set (it is without interior points) and an uncountable set (of the same cardinality as the real numbers)...

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Delone set

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discrete sets, relatively dense sets, and Delone sets (named after Boris Delone) are several closely related definitions of well-spaced sets of points...

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Dense order

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In mathematics, a partial order or total order < on a set X {\displaystyle X} is said to be dense if, for all x {\displaystyle x} and y {\displaystyle...

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Glossary of set theory

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countable collection of open dense sets is dense basic set theory 1.  Naive set theory 2.  A weak set theory, given by Kripke–Platek set theory without the axiom...

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Monotonic function

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however, do not necessarily consist of isolated points and may even be dense in an interval (a, b). For example, for any summable sequence ( a i ) (a_{i})...

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Classification of discontinuities

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it has a discontinuity there. The set of all points of discontinuity of a function may be a discrete set, a dense set, or even the entire domain of the...

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Glossary of topology

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intersection of any countable collection of dense open sets is dense; see Baire space. Baire space is the set of all functions from the natural numbers...

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List of unsolved problems in mathematics

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family of maps from the complex plane to itself is hyperbolic for an open dense set of parameters. Furstenberg conjecture – is every invariant and ergodic...

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Surfel

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is an alternative to polygonal modeling. An object is represented by a dense set of points or viewer-facing discs holding lighting information. Surfels...

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Meyer set

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In mathematics, a Meyer set or almost lattice is a relatively dense set X of points in the Euclidean plane or a higher-dimensional Euclidean space such...

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Chaos game

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iterations xk stay inside the attractor and, with probability 1, form a dense set in the latter. The "chaos game" method plots points in random order all...

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Cantor set

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ternary construction only in passing, as an example of a perfect set that is nowhere dense (, Anmerkungen zu §10, /p. 590). More generally, in topology,...

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Baire category theorem

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topological space such that the intersection of countably many dense open sets is still dense). It is used in the proof of results in many areas of analysis...

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Topological vector space

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union of compact convex sets is again compact and convex. Meager, nowhere dense, and Baire A disk in a TVS is not nowhere dense if and only if its closure...

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Sparse matrix

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contrast, if most of the elements are non-zero, the matrix is considered dense. The number of zero-valued elements divided by the total number of elements...

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Antiderivative

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{\displaystyle g(x)=G'(x)=0} for all x in the set { F ( x n ) } n ≥ 1 {\displaystyle \{F(x_{n})\}_{n\geq 1}} which is dense in the interval [ F ( − 1 ) , F ( 1...

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List of exceptional set concepts

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Nowhere dense set Null set, conull set Partition regular Piecewise syndetic set Schnirelmann density Small set (combinatorics) Stationary set Syndetic set Thick...

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List of order theory topics

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Cofinal and coinitial set, sometimes also called dense Meet-dense set and join-dense set Linked set (upwards and downwards) Directed set (upwards and downwards)...

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