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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
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An open neighborhood assignment is a function that assigns an open neighborhood to each element in the set. More formally, given a topological space
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can be created from the union of neighborhoods from the neighborhood assignment of some
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is a D-space if for every given neighborhood assignment
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may be too technical for most readers to understand
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290:. An open neighborhood assignment is a function
696:van Douwen, Eric; Lutzer, David (1997-01-01).
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516:{\displaystyle \bigcup _{x\in D}N_{x}=X}
431:, there exists a closed discrete subset
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184:make it understandable to non-experts
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595:van Douwen, E.; Pfeffer, W. (1979).
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964:Metrics and properties
950:Second-countable space
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353:{\displaystyle f(x)}
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1029:Tychonoff's theorem
1024:Poincaré conjecture
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570:space is a D-space
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986:Chern number
976:Betti number
859: /
850:Key concepts
798:Differential
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561:Menger space
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192:January 2017
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79:Please help
74:verification
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1084:Wikiversity
1001:Key results
234:mathematics
1136:Categories
930:CW complex
871:Continuity
861:Closed set
820:cohomology
685:: 107–122.
583:References
554:Properties
474:such that
266:Definition
107:newspapers
36:improve it
1109:geometric
1104:algebraic
955:Cobordism
891:Hausdorff
886:connected
803:Geometric
793:Continuum
783:Algebraic
724:0002-9939
657:162136062
490:∈
483:⋃
407:→
307:→
96:"D-space"
42:talk page
1147:Topology
1074:Wikibook
1052:Category
940:Manifold
908:Homotopy
866:Interior
857:Open set
815:Homology
764:Topology
639:Elsevier
574:it is a
537:Lindelöf
257:discrete
1099:general
901:uniform
881:compact
832:Digital
541:regular
527:History
451:of the
238:D-space
178:Please
121:scholar
1094:Topics
896:metric
771:Fields
722:
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559:Every
331:where
260:subset
254:closed
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876:Space
675:(PDF)
600:(PDF)
453:space
250:cover
240:is a
128:JSTOR
114:books
720:ISSN
653:OCLC
643:ISBN
539:and
236:, a
100:news
710:doi
706:125
612:doi
572:iff
232:In
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