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kingwinner
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Homework Statement
Give an example of a decreasing sequence of closed balls in a complete metric space with empty intersection.
Hint 1: use a metric on N topologically equivalent to the discrete metric so that {n≥k} are closed balls. In={n,n+1,n+2,...}.
Homework Equations
N/A
The Attempt at a Solution
In the following post:
https://www.physicsforums.com/showthread.php?t=374596
We showed that the metric d(m,n)=∑1/2k where the sum is from k=m to k=n-1, satisfies all the conditions required in the problem, except for completeness.
With that metric, we formed the closed balls by taking {n E N: d(k,n)≤1/2k-1} = {k-1,k,k+1,k+2,...} = Ik-1. And I1,I2,I3,... is a decreasing sequence of closed balls with empty intersection.
Now, we have to come up with another metric (possibly a modification of the above) that also satisfies completeness (i.e. every Cauchy sequence in N converges (in N)).
Does anyone have any idea?
Any help is greatly appreciated!