In a space with measure 1, ||f||p is an increasing function with respect of p. To show that limp→∞||f||p=||f||∞ we have to show that ||f||∞ is the supremum, right??
To show that, we assume that ||f||∞−ϵ is the supremum.
From the essential supremum we have that m({|f|>||f||∞−ϵ})=0.
So, we have to show that m({|f|>||f||∞−ϵ})>0.
Let A={|f|>||f||∞−ϵ}.
We have that ∫A|f|p≤∫|f|p≤||f||p∞.
∫A|f|p>∫A(||f||∞−ϵ)p=(||f||∞−ϵ)pm(A)
So, m(A)1/p(||f||∞−ϵ)<||f||p≤||f||∞
How could we continue to show that m(A)>0??
EDIT:
Is it as followed??
We have that 0<||f||∞−ϵ<||f||∞ for some ϵ>0.
||f||∞ is the essential supremum. So, from the definition we have that m({|f(x)>||f||∞−ϵ})>0.
Let A={|f|>||f||∞−ϵ}.
We have that ∫A|f|p≤∫|f|p≤||f||p∞.
∫A|f|p>∫A(||f||∞−ϵ)p=(||f||∞−ϵ)pm(A)
So, m(A)1/p(||f||∞−ϵ)<||f||p≤||f||∞
Taking the limit p→+∞ we have the following:
limp→+∞m(A)1/p(||f||∞−ϵ)<limp→+∞||f||pm(A)>0⇒limp→+∞m(A)1/p=1⟹||f||∞−ϵ<limp→+∞||f||p
Is this correct?? How do we conclude that limp→+∞||f||p=||f||∞ ??
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