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refs.bib
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refs.bib
@@ -216,11 +216,11 @@
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doi = {10.1007/BF02771592}
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}
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@MISC {StackRadonDual,
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TITLE = {How to understand C(X)'' = bounded Borel measurable functions?},
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AUTHOR = {GEdgar (https://math.stackexchange.com/users/442/gedgar)},
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HOWPUBLISHED = {Mathematics Stack Exchange},
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NOTE = {URL:https://math.stackexchange.com/q/392719 (version: 2013-05-15)},
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EPRINT = {https://math.stackexchange.com/q/392719},
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URL = {https://math.stackexchange.com/q/392719}
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@misc {StackRadonDual,
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title = {How to understand C(X)'' = bounded Borel measurable functions?},
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author = {GEdgar (https://math.stackexchange.com/users/442/gedgar)},
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howpublished = {Mathematics Stack Exchange},
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note = {URL:https://math.stackexchange.com/q/392719 (version: 2013-05-15)},
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eprint = {https://math.stackexchange.com/q/392719},
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url = {https://math.stackexchange.com/q/392719}
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}
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@@ -93,9 +93,28 @@ In any case, the above example shows that a linear functional on $M(X, \cm; \com
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\]
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\end{proof}
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Despite the fact that it does not cover the full dual space, the bounded Borel functions still forms a subspace where weak-* convergence has a convenient description.
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\begin{proposition}
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\label{proposition:measure-l-infinity-dominated-convergence}
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Let $
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Let $(X, \cm)$ be a measurable space, $E$ be a normed vector space over $K \in \RC$, and $\mathscr{M} \subset M(X, \cm; E)$ be a closed subspace such that:
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\begin{enumerate}
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\item[(P)] For each $x \in X$, $\bracs{x} \in \cm$, and the delta mass $\delta_x$ is in $\mathscr{M}$.
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\end{enumerate}
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Then, for any bounded measurable functions $\bracsn{f_n: X \to E^*|n \in \natp}$ and $f: X \to E^*$, the following are equivalent:
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\begin{enumerate}
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\item For each $\mu \in \mathscr{M}$, $\limv{n}\int f_n d\mu = \int f d\mu$.
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\item For each $x \in X$, $\limv{n}f_n(x) = f(x)$, and $\sup_{n \in \natp}\norm{f_n}_u < \infty$.
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\end{enumerate}
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\end{proposition}
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\begin{proof}
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(1) $\Rightarrow$ (2): By (P), for each $x \in X$, $\limv{n}f_n(x) = f(x)$. By the \hyperref[Uniform Boundedness Principle]{theorem:uniform-boundedness},
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\[
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\sup_{n \in \natp}\norm{f_n}_u \le \sup_{n \in \natp}\norm{f_n}_{\mathscr{M}^*} < \infty
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\]
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(2) $\Rightarrow$ (1): By the \hyperref[Dominated Convergence Theorem]{theorem:dct-bochner-vector}.
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\end{proof}
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