- Countable tightness
In
mathematics , atopological space is said to have countable tightness if it satisfies the condition::Given any subset , if , there is a countable subset such that .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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