Proving Connectivity of B & cl(A)

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Homework Help Overview

The discussion revolves around proving the connectivity of a subset B that lies between a connected set A and its closure cl(A) in a topological space. The original poster seeks to establish that if A is connected and A is a subset of B, then B must also be connected.

Discussion Character

  • Conceptual clarification, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants explore the implications of assuming B can be expressed as a disjoint union of two nonempty open sets. There is an attempt to use a contrapositive approach, although uncertainty exists regarding the nature of G and H as open sets in the topological space.

Discussion Status

Participants are actively engaging with the problem, questioning the assumptions about the openness of sets and exploring the relationship between B and A. Some guidance has been offered regarding the implications of B's disconnection on A's connectivity, but no consensus has been reached on the approach to take.

Contextual Notes

There is a noted uncertainty about whether the discussion is taking place within a topological space context, which may affect the interpretation of the sets involved. Additionally, the original poster is grappling with how to effectively use the properties of connectedness in their argument.

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Homework Statement


Let A be connected subset of X and let A ⊂ B ⊂ cl(A). Show that B is connected and hence, in particuar, cl(A) is connected.

Hint: (Use) Let G∪H be a disconnection of A and let B be a connected subset of A then we see that either B∩H=∅ or B∩G=∅, and so either B⊂G or B⊂H.




2. The attempt at a solution
ı try to use contrapositive method but ı can't find a solution exactly.. ım not sure that we work in topological space (and are G and H open in X)
 
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Thanks grey_earl but I want to show if A is connected set and A ⊂ B ⊂ cl(A) then B is connected..
I have to show that ""Suppose B=G∪H is a disconnection of B, then using the fact that B ⊂ cl(A) prove that contradict the given A is connected""
How can I show this?
 
So B is the disjoint union of nonempty open sets G and H. Can you show that [tex]A\cap G[/tex] and [tex]A\cap H[/tex] forms a disconnection of A? Thus in particacular, A is the disjoint union on nonempty open sets.
 

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