Example: intersection of compact sets which is NOT compact

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Homework Help Overview

The problem involves finding subsets M_1 and M_2 that are compact within a specific topology defined on the real line, where the topology is generated by a base S. The challenge is to demonstrate that while both subsets are compact, their intersection is not.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the definition of compactness and its implications in the context of the given topology. There is uncertainty about the meaning of compactness in this specific setting, and some participants seek clarification on foundational terms such as 'open set', 'cover', and 'finite subcover'.

Discussion Status

The discussion is ongoing, with participants exploring definitions and seeking to clarify their understanding of compactness and the topology involved. Some foundational concepts have been confirmed, but there is no consensus on how to proceed with the problem itself.

Contextual Notes

There is a noted uncertainty regarding the interpretation of compactness in the context of the topology defined by the base S, and the participants are working within the constraints of the definitions provided in the problem statement.

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Homework Statement


Let S = {(a,b) : 0 < a < b < 1 } Union {R} be a base for a topology. Find subsets M_1 and M_2 which are compact in this topology but whose intersection is not compact.

Homework Equations


The Attempt at a Solution


I'm not even sure what it means for an element of S to be compact, so I haven't been able to make any attempt at a solution.
 
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I assume you're working on the real line, right?

Do you know the meaning of the terms 'open set', 'cover' and ' finite subcover'?
I don't mean to be condescending; just to know.
 
I assume it is the real line, and so the topological space will be (R,S).

Yes I do know what open set/cover/finite sub cover mean
 
The most general definition is that a subset S is compact iff (def.) every cover of S by open sets has a finite subcover. There are more specialized results, e.g., for R^n, compactness is equivalent to being closed and bounded,and, for metric spaces you have, e.g., every sequence has a convergent subsequence, but the first one covers all cases.
 

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