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修改错误
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EdmundWhis committed Mar 20, 2020
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10 changes: 5 additions & 5 deletions Appendix_B.tex
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Expand Up @@ -650,11 +650,11 @@ \section{第3章习题}
\item$ f\in\bigcap_{p<\infty}L_p(X) $且满足$ \limsup\limits_{p\to\infty}\norm{f}_p<\infty $, 证明$ f\in L_\infty(X) $.
\end{enumerate}
\begin{Proof}
(1) 若$ q=\infty $, 结论显然成立, 下设$ p<\infty $. 取$ p'=q/p $$ q'=q/(q-p) $, 那么$ 1/p+1/q=1 $. 由H\"older不等式可知
(1) 若$ q=\infty $, 结论显然成立, 下设$ p<\infty $. 取$ p'=q/p $$ q'=q/(q-p) $, 那么$ 1/p'+1/q'=1 $. 由H\"older不等式可知
\[
\begin{aligned}
\norm{f}_p^p=\int_X\abs{f}^p\diff\mu&=\int_X\abs{f}^p\cdot 1\diff\mu\\
&\leqslant\norm{\abs{f}^p}_{p'}\norm{1}_{q'}=\int_X(\abs{f}^p)^{q/p}\diff\mu\cdot\mu(X)^{q'}=\norm{f}_q^p\cdot\mu(X)^{q'}.
\norm{f}_p^p&=\int_X\abs{f}^p\diff\mu=\int_X\abs{f}^p\cdot 1\diff\mu=\norm{\abs{f}^p\cdot 1}_1\\
&\leqslant\norm{\abs{f}^p}_{p'}\cdot\norm{1}_{q'}=\left(\int_X(\abs{f}^p)^{p'}\right)^{1/p'}\mu(X)^{1/q'}=\norm{f}_q^p\cdot\mu(X)^{1/q'}
\end{aligned}
\]
$ \norm{f}_p\leqslant\norm{f}_q\cdot\mu(X)^{1/p-1/q} $, 从而$ \norm{f}_q<\infty\Longrightarrow\norm{f}_p<\infty $, 即$ L_q(X)\subset L_p(X) $.
Expand Down Expand Up @@ -1036,11 +1036,11 @@ \section{第5章习题}

\textbf{习题5.1}\ [习题课]\ \ 对任意$ x\in[0,1] $, 设$ f_n(x)=x^n $. 在$ [0,1] $的哪些点处, $ (f_n)_{n\geqslant 1} $等度连续?
\begin{Proof}
对任意的$ x\in[0,1) $, 有
对任意的$ a\in[0,1) $, 有
\[
\abs{x^n-a^n}=\abs{(x-a)(x^{n-1}+x^{n-2}a+\cdots+a^{n-1})}\leqslant(1+a+\cdots+a^{n-1})\abs{x-a}<\frac{\abs{x-a}}{1-a},
\]
$ (f_n)_{n\geqslant 1} $$ x\in[0,1) $上等度连续. 但$ x=1 $时, 因为对任意的$ x\in(1-\delta,1) $, 有
$ (f_n)_{n\geqslant 1} $$ x\in[0,1) $上等度连续. 但$ a=1 $时, 因为对任意的$ x\in(1-\delta,1) $, 有
\[
\lim_{n\to\infty}\abs{f_n(x)-f_n(1)}=1,
\]
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2 changes: 1 addition & 1 deletion Appendix_B2.tex
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Expand Up @@ -279,7 +279,7 @@ \section{第8章习题}
\[
\tilde{f} = x_{1}\tilde{f}(e_{1})+x_{2}\tilde{f}(e_{2})=x_{1}+x_{2}\tilde{f}(e_{2}),
\]
$ \tilde{f} $ 由其在 $ e_{2} $ 上的取值唯一确定, 记 $ c=\tilde{f}(e_{2}) $, 由 $ \tnorm{\tilde{f}}=1 $$ \abs{c}=\tabs{\tilde{f}(e_{2})}\leqslant\norm{e_{2}}=1 $. 反之, 对任意的 $ c $ 满足 $ \abs{c}<1 $, 形如 $ \tilde{f}(x)=x_{1}+x_{2}c $ 的泛函是 $ f $ 的保范延拓.
$ \tilde{f} $ 由其在 $ e_{2} $ 上的取值唯一确定, 记 $ c=\tilde{f}(e_{2}) $, 由 $ \tnorm{\tilde{f}}=1 $$ \abs{c}=\tabs{\tilde{f}(e_{2})}\leqslant\norm{e_{2}}=1 $. 反之, 对任意的 $ c $ 满足 $ \abs{c}\leqslant 1 $, 形如 $ \tilde{f}(x)=x_{1}+x_{2}c $ 的泛函是 $ f $ 的保范延拓.

(2) 当 $ 1<p<\infty $ 时, 与 (1) 同理, 只需确定 $ c $ 使 $ \tnorm{\tilde{f}}=1 $, 则
\[
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