In a space with measure 1, ||f||p is an increasing function with respect of p. To show that lim we have to show that ||f||_{\infty} is the supremum, right??
To show that, we assume that ||f||_{\infty}-\epsilon is the supremum.
From the essential supremum we have that m(\{|f|>||f||_{\infty}-\epsilon\})=0.
So, we have to show that m(\{|f|>||f||_{\infty}-\epsilon\})>0.
Let A=\{|f|>||f||_{\infty}-\epsilon\}.
We have that \int_A |f|^p \leq \int |f|^p \leq ||f||_{\infty}^p.
\int_A |f|^p >\int_A (||f||_{\infty}-\epsilon)^p=(||f||_{\infty}-\epsilon)^p m(A)
So, m(A)^{1/p} (||f||_{\infty}-\epsilon)<||f||_p \leq ||f||_{\infty}
How could we continue to show that m(A)>0??
EDIT:
Is it as followed??
We have that 0<||f||_{\infty}-\epsilon<||f||_{\infty} for some \epsilon>0.
||f||_{\infty} is the essential supremum. So, from the definition we have that m\left ( \{|f(x)>||f||_{\infty}-\epsilon\} \right )>0.
Let A=\{|f|>||f||_{\infty}-\epsilon\}.
We have that \int_A |f|^p \leq \int |f|^p \leq ||f||_{\infty}^p.
\int_A |f|^p >\int_A (||f||_{\infty}-\epsilon)^p=(||f||_{\infty}-\epsilon)^p m(A)
So, m(A)^{1/p} (||f||_{\infty}-\epsilon)<||f||_p \leq ||f||_{\infty}
Taking the limit p \rightarrow +\infty we have the following:
\lim_{p \rightarrow +\infty}m(A)^{1/p} (||f||_{\infty}-\epsilon)<\lim_{p \rightarrow +\infty} ||f||_p \overset{ m(A)>0 \Rightarrow \lim_{p \rightarrow +\infty}m(A)^{1/p}=1}{\Longrightarrow} \\ ||f||_{\infty}-\epsilon<\lim_{p \rightarrow +\infty} ||f||_p
Is this correct?? How do we conclude that \lim_{p \rightarrow +\infty} ||f||_p=||f||_{\infty} ??
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