Is the Component of a Metric Space Always Open or Closed?

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Discussion Overview

The discussion revolves around the nature of connected components in metric spaces, specifically whether they can be open, closed, both, or neither. Participants explore the definitions and properties of connected components, particularly in the context of real numbers and intervals.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions whether a component of a metric space can be open, closed, both, or even half-open, citing the interval (3,5] as an example.
  • Another participant asserts that a connected component is always closed but may not be open.
  • A subsequent reply agrees that a connected component is always closed but points out that (3,5] is not closed in R.
  • Another participant clarifies that (3,5] is not a component because R itself is connected and thus is the component.
  • Further discussion includes the assertion that every interval in R is connected but not necessarily a maximal connected set, with R being the maximal connected set.

Areas of Agreement / Disagreement

Participants generally agree that connected components are closed but disagree on the status of specific intervals like (3,5] as components, leading to unresolved questions about the nature of components in metric spaces.

Contextual Notes

There is a lack of consensus on the definitions of components and maximal connected sets, and the discussion highlights the need for clarity regarding these concepts in the context of metric spaces.

jessicaw
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Is component(maximal connected set) of a metric space open or closed or both(clospen)?or even can be half-open(not open and not closed)?
I know it is a silly question as (3,5] is a component in R,right?
However some theorem i encountered stated that component must be closed or must be open. I know they can't be contradictory but i need help in understanding this. Thx~
 
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A connected component is always closed, but may not be open.
 
Eynstone said:
A connected component is always closed, but may not be open.

BUT (3,5] is not closed on R, right?
 
No, it is not closed. But it's not a component to. R itself is connected, thus R itself is the component.
 
so interval in R1 is in the form [x,y]?
 
I'm not sure what you mean...

Every interval (wether it is [a,b], [a,b[, ]a,b], ...) is connected in R. But they are not components, since they are not MAXIMAL connected sets. Indeed, R itself is connected and is thus the maximal connected set. Thus R itself is a component. The intervals are not components, but are connected...
 

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