Comparing Finite Complement and (-inf,a) Topologies: Are T_3 and T_5 Comparable?

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Homework Help Overview

The discussion revolves around comparing two specific topologies on the real numbers: the finite complement topology, T_3, and the topology generated by sets of the form (-inf, a), denoted as T_5. Participants are exploring whether these topologies are comparable in terms of their structure and properties.

Discussion Character

  • Conceptual clarification, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to determine the comparability of T_3 and T_5, having established that T_3 is not strictly finer than T_5, but is uncertain about the reverse relationship. Some participants question the definitions and properties of the topologies involved, particularly regarding the inclusion of certain sets in T_5 and the nature of basis elements in T_3.

Discussion Status

The discussion is active, with participants providing insights and raising questions about the definitions and relationships between the topologies. There is a focus on clarifying the properties of T_3 and T_5, and some guidance has been offered regarding specific sets and their membership in the respective topologies.

Contextual Notes

Participants are navigating potential misunderstandings related to the definitions of the finite complement topology and the basis for T_5. There is also mention of additional topologies, such as T_2 and T_4, which may complicate the discussion further.

Nusc
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I need to show if the finite complement topology,T_3, and the topology having all sets (-inf,a) = {x|x<a} as basis ,T_5, are comparable.

I've shown that T_3 is not strictly finer than T_5.

But I'm not sure about other case.

I need help.
 
Last edited by a moderator:
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I presume you're defining these topologies on R and that you managed to find a set in T_5 that's not in T_3. The other direction is just as easy: is R\{0} in T_5?
 
R\{0} is not in T_5. (-inf,0]U[0,inf)

If T_4 is the upper limit topology, having the sets (a,b] as a basis and
T_2 the topology of R_K (a,b)-K K = 1/n n in Z.

I've shown that T_2 is not strictly finer than T_4.
How do I show that T_4 is strictly finer than T_2?
 
Last edited:
And most importantly, why is R\{1,2,3} considered a basis element for T_3?

It's not finite, nor is it all of R. I'm confused with the definition of a finite complement topology.
 
Topology

Is {1} = (0,2) ?
and R\{0} = (-inf,0]U[0,inf) ?
 
Last edited:
Note: I have merged your two threads on this since you had already received responses in the Calc and Analysis forum.
 
Hello?
 
Look at morphism's post!
 

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