How Do Nonempty Closed Sets Intersect in Compact Spaces?

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Euge
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Here is this week's POTW:

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Prove that in a compact topological space, any decreasing sequence of nonempty closed sets has non-empty intersection.

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  • #2
Congratulations to castor28 for his correct solution, which is as follows:
Let $E$ be a compact topological space and $\{A_i\}$ a decreasing sequence of non-empty closed sets; $A_i^c$ is therefore an increasing sequence of open proper subsets of $E$.

Assume that $\bigcap A_i= \emptyset$. $\bigcup A_i^c=E$, and the $A_i$ constitute an open cover of $E$. As $E$ is compact, $\{A_i^c\}$ contains a finite sub-cover $\{A_{i_1}^c,\ldots,A_{i_n}^c\}$ whose union is $E$. As the $A_i^c$ constitute an increasing sequence, we have $ A_{i_n}^c=E$, and this contradicts the fact that the $A_i^c$ are proper subsets (because the $A_i$ are non-empty sets).
 

FAQ: How Do Nonempty Closed Sets Intersect in Compact Spaces?

1. What is POTW?

POTW stands for "Problem of the Week," which is a challenge or puzzle presented to scientists or researchers to solve.

2. What is the purpose of POTW?

The purpose of POTW is to encourage critical thinking and problem-solving skills among scientists and researchers. It also allows for the exchange of ideas and collaboration within the scientific community.

3. How often is POTW presented?

POTW is typically presented on a weekly basis, hence the name "Problem of the Week." However, it may vary depending on the organization or platform that presents it.

4. How is the solution to POTW determined?

The solution to POTW is determined by evaluating the accuracy and validity of the proposed solution by scientists or researchers. This can be done through experiments, calculations, or other scientific methods.

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Some organizations or platforms may offer rewards for solving POTW, such as recognition or prizes. However, the main purpose of POTW is to challenge and stimulate scientific thinking, rather than to receive rewards.

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