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D-space

From Wikipedia, the free encyclopedia

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In mathematics, a D-space is a topological space where for every neighborhood assignment of that space, a cover can be created from the union of neighborhoods from the neighborhood assignment of some closed discrete subset of the space.

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Definition

An open neighborhood assignment is a function that assigns an open neighborhood to each element in the set. More formally, given a topological space . An open neighborhood assignment is a function where is an open neighborhood.

A topological space is a D-space if for every given neighborhood assignment , there exists a closed discrete subset of the space such that .

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History

The notion of D-spaces was introduced by Eric Karel van Douwen and E.A. Michael. It first appeared in a 1979 paper by van Douwen and Washek Frantisek Pfeffer in the Pacific Journal of Mathematics.[1] Whether every Lindelöf and regular topological space is a D-space is known as the D-space problem. This problem is among twenty of the most important problems of set theoretic topology.[2]

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References

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