Suppose I have a set equipped with two equivalent metrics, and , meaning that the metrics induce the same topology on . I know that and need not be comparable on all of , however, is it true that they will be comparable on compact subsets of ?

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- Aug 17th 2010, 04:38 AMyoyomaAre equivalent metrics comparable on compact sets?
Suppose I have a set equipped with two equivalent metrics, and , meaning that the metrics induce the same topology on . I know that and need not be comparable on all of , however, is it true that they will be comparable on compact subsets of ?

- Aug 18th 2010, 07:35 AMIondor
No, they aren't.

Consider the cantor space , which is the product space of the discrete space {0,1}.

It is compact and induced by two incomparable metrices

, where is the smallest i , such that

Then there is no constant K such that

for all x,y. - Aug 18th 2010, 08:23 AMyoyoma
Thanks for your reply. May I also ask, what about in the situation where the distance functions and are induced by a Riemannian metric on a smooth manifold? In this case the topologies induced by and each agree with the manifold topology, but these distance functions need not be comparable on the entire manifold. However, will they be comparable on compact subsets of the manifold?