If you have a decreasing sequence of compact subsets of X such that C1⊃C2⊃... Cm and C=∩∞,m=1, then show that the Hausdorff metric, D(Cn,C)→0 as n→∞.

Assume C∈S(X)

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- February 2nd 2010, 10:56 AMSamBourneHelp with fractals
If you have a decreasing sequence of compact subsets of X such that C1⊃C2⊃... Cm and C=∩∞,m=1, then show that the Hausdorff metric, D(Cn,C)→0 as n→∞.

Assume C∈S(X) - February 2nd 2010, 11:32 AMOpalg
Since C is the intersection of the s, it is sufficient to find a value of m for which every element of is within distance of C (for some given ).

Let . This is a closed (and therefore compact) subset of . It is covered by the sets , which are open in . By compactness there is a finite subcover, and since the sets form an increasing nest, there is in fact just one of them, say , that contains . It follows by taking complements that . Thus .