Can Non-Compact Closed Subsets Be Disjoint in a Metric Space?

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SUMMARY

The discussion centers on identifying non-compact closed subsets in a metric space that are disjoint yet have points arbitrarily close to each other. The participants explored the metric space of infinite binary sequences, concluding that it is compact, which contradicts the requirement for non-compact subsets. They also noted that the Euclidean space R² is non-compact and suggested that graphs of continuous functions from R to R are closed, indicating potential avenues for examples that meet the criteria.

PREREQUISITES
  • Understanding of metric spaces and their properties
  • Familiarity with concepts of compactness and closed sets
  • Knowledge of infinite sequences and convergence
  • Basic principles of topology, particularly in R²
NEXT STEPS
  • Research examples of non-compact closed subsets in R²
  • Study the properties of graphs of continuous functions in metric spaces
  • Explore the concept of convergence in infinite-dimensional spaces
  • Investigate the implications of compactness in various metric spaces
USEFUL FOR

Mathematicians, students of topology, and anyone studying metric spaces and their properties will benefit from this discussion.

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Homework Statement



Give an example of a metric space [itex](X,d)[/itex], and nonempty subsets A,B of X such that both A,B are closed, non-compact, disjoint ([itex]A \cap B = \emptyset[/itex]), and [itex]\forall k>0, \; \exists a \in A, b \in B[/itex] such that d(a,b)<k

The Attempt at a Solution



I've been trying to consider the set of all infinite binary sequences
[tex]X = \left\{ (x^{(1)}, x^{(2)}, \ldots, x^{(n)}, \ldots ) | x^{(i)} \in \{0,1\} \forall i \geq 1 \right\}[/tex]

but I ended up showing that this is a compact metric space and as such all closed subsets are necessarily compact.

So I'm not terribly sure about any other examples that might work...

Edit: X is a compact metric space under

[tex]d(x,y) = \displaystyle \sum_{k=1}^\infty \frac{1}{2^k} | x^{(k)} - y^{(k)} |[/tex]
 
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R^2 is not compact. And graphs of continuous functions R->R are closed. Does that suggest anything?
 

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