how does one go about showing that a set is open/closed.
e.g the set below is said tobe closed for finite values of T. but not closed for T=
how can we show that?
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First, you need to be perfectly clear about the topological space in which this whole problem statement is to be situated.
If it is a metric space you can do the following:
1. To show thatis closed (for
) you show that the limit
of any convergent sequence of functions
also lies in
.
2. To show thatis not closed (for
) you show that there exists a sequence of functions
in
, the limit
of which does not lie in
. (For example: it is easy to find a sequence of functions
with limit
.)
I'm not sure what the problem is asking for specifically. In general, to show a set is closed, you want to show its complement is open. Are you asking whether and why the set, specifically, is closed? I assume so. (Give enough detail with your problem!)
I suppose the integral is the usual Riemann integral andis Riemann-integrable on every compact subset of
. Then
is continuous, and for any continuous function
, and any
, the set
is closed. (Prove this! Just apply the definition of continuity.)