Uniformity of Space: Definition & Examples

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Discussion Overview

The discussion centers around the concept of "uniformity" in the context of topology, specifically regarding the properties of spaces where neighborhoods exhibit certain homeomorphic characteristics. Participants explore the definitions and implications of these properties, questioning the equivalence of different statements about homeomorphisms and continuity.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the terminology related to spaces where neighborhoods are homeomorphic, suggesting that such spaces may be considered uniform, although they acknowledge that "uniform space" has a distinct meaning.
  • Another participant challenges the equivalence of two statements regarding homeomorphisms, asserting that a continuous bijection does not guarantee homeomorphic neighborhoods without a continuous inverse.
  • A later reply acknowledges the correction regarding the equivalence of the statements and indicates an intention to update their understanding.
  • One participant argues that a continuous bijection should suffice for the properties discussed, explaining the implications of continuity and bijection in the context of open sets.
  • However, they also raise a concern that the assumption that all open sets can be expressed in a certain form may not hold true.

Areas of Agreement / Disagreement

Participants express disagreement regarding the equivalence of the two statements about homeomorphisms and continuity, indicating that the discussion remains unresolved on this point.

Contextual Notes

There are limitations in the assumptions made about the nature of open sets and the conditions under which homeomorphisms apply, which remain unresolved in the discussion.

alexfloo
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"Uniformity" of space

I have a question about terminology. Suppose we have a space X with the property that:

for all x, x' in X and neighborhood N of x, N is homeomorphic to some neighborhood N' of x'
OR
for all x, x' there exists a homeomorphism f:X→X s.t. f(x)=x'.

(I believe these are equivalent, but I haven't worked it out.) In some sense, these spaces are uniform (although I know that uniform space has its own meaning). There are no "distinguished" points, or different "types" of points. (Any open, simply-connected subset of Euclidean space has this property. Any closed subset of Euclidean space not equal to its boundary lacks it, since boundary points cannot be continuously mapped onto interior points.)

Is there a name for this?

EDIT: fixed an error.
 
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actually those 2 sentences are not equivalent since the continuous bijection doesn't guarantee the homeomorpic between neighborhood of x and x' , it must have continuous inverse to be homeomorphic
 


EDIT: You are correct. I'll add that in.
 


alexfloo said:
Continuous bijection should be sufficient:

Continuous X→Y means for each open OY subset of Y, f-1(OY)=OX is open in X. Bijection means that

f(OX)=f(f-1(OY))=OY,

so f-1 is also continuous.

Now you assume that all open sets are of the form f^{-1}(O_Y). This is not necessarily true.
 

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