another proof of Dini’s theorem
This is the version of the Dini’s theorem I will prove:Let be a compact
metric space and which converges
pointwise to .
Besides, .
Then converges uniformly in .
Proof
Suppose that the sequence does not converge uniformly. Then, by definition,
So,
Then we have a sequence and is a subsequence of the original sequence of functions. is compact, so there is a subsequence of which converges in , that is, such that
I will prove that is not continuous in (A contradiction
with one of the hypothesis
).
To do this, I will show that does not converge to , using above’s .
Let ,which exists due to the punctual convergence of the sequence. Then,particularly, .
Note that
because (using the hypothesis ) it’s easy to see that
Then, . And also the hypothesis implies
So, which implies
Now,
and so
On the other hand,
And as is continuous, there is a such that
Then,
which implies
Then, particularly, does not converge to . QED.