Showing Range of Sequence in Metric Space is Not Always Closed

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Homework Help Overview

The discussion revolves around the properties of the range of a sequence in a metric space, specifically addressing whether such a range is a closed set. The original poster seeks to understand the conditions under which a sequence's range may or may not be closed.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants explore examples of convergent sequences and their properties regarding closed sets. There is a focus on contrasting different sets derived from sequences to illustrate the concept.

Discussion Status

The discussion includes attempts to clarify the definitions and properties of closed sets in the context of sequences. Some participants provide examples to differentiate between closed and non-closed sets, indicating a productive exploration of the topic.

Contextual Notes

There is an emphasis on understanding the implications of convergence and the nature of the sequences in question, with some participants questioning the assumptions about what constitutes a closed set in metric spaces.

yifli
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Homework Statement


show that (the range of) a sequence of points in a metric space is in general not a closed set. Show that it may be a closed set.


2. The attempt at a solution
I don't know where to start.
For example, if we are given a sequence of real numbers and the distance between a and b is defined as |a-b|, it asks us to show that a sequence of real numbers is in general not a closed set?
 
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Pick your favorite convergent sequence. Is this a closed set?
 
Note the difference between the sets {1, 1/2, 1/3,..., 1/n,...} and {0, 1, 1/2, 1/3, 1/4, ..., 1/n, ...}
 
HallsofIvy said:
Note the difference between the sets {1, 1/2, 1/3,..., 1/n,...} and {0, 1, 1/2, 1/3, 1/4, ..., 1/n, ...}

thank you. I can see {1, 1/2, 1/3,...} is not closed, but {0,1,1/2,1/3,...} is.
 

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