Finite Complement Topology: Why It's the Finest

  • Context: Graduate 
  • Thread starter Thread starter beetle2
  • Start date Start date
  • Tags Tags
    Topology
Click For Summary

Discussion Overview

The discussion revolves around the finite complement topology, specifically exploring why it qualifies as a topology and whether it is considered the finest topology. Participants engage with concepts from point-set topology, examining properties and definitions related to this topology.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants inquire about resources that explain why the finite complement topology is indeed a topology.
  • One participant suggests that demonstrating the properties of the finite complement topology involves tedious exercises in point-set topology, specifically using DeMorgan's laws.
  • Another participant mentions the need for conditions to determine whether a topology is the finest, noting that definitions of "finer topology" can vary among different sources.
  • There is a discussion about the relationship between the finite complement topology and the discrete topology, with one participant asserting that the discrete topology is the finest topology in any space.
  • Participants explore the implications of intersections and unions of sets within the context of the finite complement topology, questioning the conditions under which these operations hold.

Areas of Agreement / Disagreement

Participants express differing views on the definition of the finest topology and the conditions necessary to establish this. There is no consensus on the specific criteria or implications of the finite complement topology being the finest.

Contextual Notes

Participants highlight the potential ambiguity in the term "finest topology" and the need for clarity regarding definitions and conditions. There are also unresolved mathematical steps related to the properties of intersections and unions in the context of the finite complement topology.

beetle2
Messages
110
Reaction score
0
Hi Guys
I was wondering if anyone knows of a good link that shows why the finite complement is a Topology?
I been told it is the finest topology is this right?
 
Physics news on Phys.org
Beetle2 (Is that Paul?. Ringo.?. John.?George.?)
" Hi Guys
I was wondering if anyone knows of a good link that shows why the finite complement is a Topology? I been told it is the finest topology is this right? "

I think it is a good, tho maybe a little tedious exercise in point-set topology:

1)Let A1,A2 be in cofinite, so that X-A1, X-A2 is finite. Using DeMorgan:

(X-A1)\/(X-A2)=X-(A1/\A2) . Can you see why X-( X-(A1/\A2)) is in (X,T), or why


any union of sets in (X,T) is in (X,T).?


2) (X-A1)/\(X-A2)=(X-(A1\/A2)). What happens with X-(X-(A1\/A2)).? (Can you see

why you need finitely-many Xn's here.?
 
Forgot to add a few things:

I think you need to add some conditions to state whether a topology is finest

or not (maybe with respect to some map being continuous, e.g.)

Depending on your definition of finer topology ( unfortunately, I have seen that

different people mean opposite things by this term), the finest topology in a

space X is given by 2^X --the discrete topology--and the coarser one is given

by (X, empty.)
 
1)Let A1,A2 be in cofinite, so that X-A1, X-A2 is finite. Using DeMorgan:

(X-A1)\/(X-A2)=X-(A1/\A2) . Can you see why X-( X-(A1/\A2)) is in (X,T)


Is it because X-( X-(A1/\A2)) = A1/\A2 and the intercection of any closed sets in T1 is a finite set.
 
Last edited:
It's straightforward, just remember De Morgan's laws for sets.
 
Last edited:

Similar threads

  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 1 ·
Replies
1
Views
5K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 15 ·
Replies
15
Views
3K
  • · Replies 47 ·
2
Replies
47
Views
4K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 12 ·
Replies
12
Views
1K
  • · Replies 2 ·
Replies
2
Views
6K