Closed Set Requirements

Folks,

Generally speaking, what must I use to show that a certain set of elements is a closed subset of some other larger set for a certain norm?

Thanks

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Originally Posted by bugatti79

Generally speaking, what must I use to show that a certain set of elements is a closed subset of some other larger set for a certain norm?

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Is this a question about a general topological space?
You used the word norm. Does that imply that this is a metric space?

Or is the some other setting altogether for closed subsets of elements?

Quote:

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Originally Posted by Plato

Is this a question about a general topological space?
You used the word norm. Does that imply that this is a metric space?

Or is the some other setting altogether for closed subsets of elements?

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Yes, I am referring to a metric space....... (I suspect the question is too vague for a reasonable answer.)

Thanks Plato.

Quote:

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Originally Posted by bugatti79

Yes, I am referring to a metric space....... (I suspect the question is too vague for a reasonable answer

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Two general approaches come to mind at once.
First, show that the set contains all of its limit points.

Second, equivalently show that its complement is open.

Quote:

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Originally Posted by Plato

Two general approaches come to mind at once.
First, show that the set contains all of its limit points.

Second, equivalently show that its complement is open.

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For this example...is the set



a closed subset in C[a,b] with the integral norm?

How would i tackle this?

thanks