Question about elementary topology

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    Elementary Topology
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Discussion Overview

The discussion centers around the properties of closed sets in the context of product topologies, specifically whether the product of closed sets is closed in both finite and infinite product topologies.

Discussion Character

  • Technical explanation, Debate/contested

Main Points Raised

  • One participant asks whether the product of closed sets is closed in the product topology, expressing initial confidence in a positive answer.
  • Another participant suggests using the fact that the closure of the product is the product of the closures, implying a connection to the question.
  • A different participant notes that while the statement holds true for finite products, there is uncertainty regarding its validity for infinite products, highlighting the need for a different basis in that case.
  • A later reply indicates agreement with the previous point and suggests that the reasoning can be applied to infinite cases as well.
  • Another participant asserts that it is indeed true for infinite products and mentions that there is a simple proof, although the details of this proof are not provided.

Areas of Agreement / Disagreement

There is some agreement that the product of closed sets is closed for finite products, but uncertainty remains regarding infinite products, with differing views on the applicability of the reasoning to that case.

Contextual Notes

The discussion does not resolve the question for infinite products, and the assumptions regarding the nature of the topological spaces involved are not fully explored.

facenian
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Hello, I've got a simple question
is the product of closed sets closed in the product topology?
I think the answer is yes but need to sure
 
Last edited:
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Use the fact for product topologies that the closure of the product is the product of the closures.
 
It is true for finite product, but I am not so sure it is true for infinite products.

For a product of finitely many spaces, the base is given by the product of
all open sets , i.e., given spaces X_1,..,X_n , and U_i open in X_i , then
U_1 xU_2 x...xU_n is open in the product and a basis element.

For infinite products, you need a different basis.
 
Thank you guys, I think we can use what VeeEight says which true for the infinite casa as well
 
Yes, it is true for infinite products and is a simple proof. Hope that helps.
 

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