Countable tightness

Countable tightness

In mathematics, a topological space X is said to have countable tightness if it satisfies the condition::Given any subset A subset X, if x in overline{A}, there is a countable subset B subset A such that x in overline{B}.

A prototypical example of such a space is a sequential space.

References

* [http://www.projecteuclid.org/DPubS/Repository/1.0/Disseminate?view=body&id=pdf_1&handle=euclid.bams/1183554649 Countable tightness and proper forcing]


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