Another similar notion to compactness

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SUMMARY

The discussion explores an alternative perspective on compactness in general topology, focusing on covering a set by finite intersections of closed sets rather than finite unions of open sets. It clarifies that any set can be represented as the intersection of a finite number of closed sets by taking its closure, and that the closure itself is the intersection of all closed sets containing the set. The finite intersection property is identified as the established concept related to this idea, directly linked to compactness as detailed on the Wikipedia page for the finite intersection property.

PREREQUISITES

  • General Topology: Definitions of open and closed sets
  • Compactness in Topology: Open cover and finite subcover concepts
  • Finite Intersection Property in Topology
  • Set Closure and Intersection Operations

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  • Study the Finite Intersection Property and its equivalence to compactness
  • Review the role of closed sets in defining compact spaces
  • Explore alternative characterizations of compactness in different topological spaces
  • Analyze examples of compact and non-compact spaces using closed set intersections

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Students and researchers in general topology, mathematicians studying compactness properties, and anyone interested in alternative formulations and deeper understanding of compactness and closure operations in topological spaces.

mad mathematician
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I really don't understand why I didn't think about it while I learned UG topology back then.

The usual definition of Compactness is that every open cover of the compact space can be covered by a finite union from the arbitrary cover.

What about looking at a set that is covered by the intersection of a finite number of closed sets, from which we can cover by any number of closed sets' interesection?

I.e, if ##X=\cap_{i=1}^n F_i## then one can cover ##X## by an intersection of any number of closed sets.

Is there such a notion? is it too trivial? too strong?
 
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Any set can be covered by a finite intersection of closed sets; simply take its closure. Furthermore, the closure of a set is itself the intersection of all closed sets containing it.
 
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