Added the algebraic tensor product.

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Bokuan Li
2026-03-18 14:16:55 -04:00
parent f25600cbd3
commit fdd4d752e9
4 changed files with 107 additions and 1 deletions

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@@ -44,6 +44,8 @@
\end{proof}
\begin{theorem}[Dominated Convergence Theorem]
\label{theorem:dct-bochner}
Let $(X, \cm, \mu)$ be a measure spacs, $E$ be a Banach space over $K \in \RC$, $\seq{f_n} \subset L^1(X; E)$, and $f \in L^1(X; E)$. If
@@ -58,3 +60,48 @@
By the classical \hyperref[Dominated Convergence Theorem]{proposition:dct-lp}, $f_n \to f$ in $L^1(X; E)$. Since $h \mapsto \int h d\mu$ is a bounded linear operator, $\int f d\mu = \limv{n}\int f_n d\mu$.
\end{proof}
\subsection{Vector Measure Version}
\label{subsection:bochner-vector}
\begin{definition}[Bochner Integral]
\label{definition:bochner-integral-vector}
Let $(X, \cm)$ be a measurable space, $E, F$ be normed spaces over $K \in \RC$, $G$ be a Banach space over $K$,
\[
\lambda: E \times F \to G \quad (x, y) \mapsto xy
\]
be a bounded bilinear map, and $\mu: \cm \to F$ be a vector measure, then there exists a unique $I_\lambda \in L(L^1(X, |\mu|; E); G)$ such that:
\begin{enumerate}
\item For any $x \in E$ and $A \in \cm$, $I_\lambda(x \cdot \one_A) = x \mu(A)$.
\item For any $f \in L^1(X, |\mu|; E)$, $\normn{I_\lambda f}_{G} \le \norm{\lambda}_{L^2(E, F; G)} \cdot \norm{f}_{L^1(X, |\mu|; E)}$.
\end{enumerate}
For any $f \in L^1(X; E)$, $I_\lambda f = \int f d\lambda\mu$ is the \textbf{Bochner integral} of $f$ with respect to $\mu$ and $\lambda$.
\end{definition}
\begin{proof}
Same as \autoref{definition:bochner-integral}.
\end{proof}
\begin{theorem}[Dominated Convergence Theorem]
\label{theorem:dct-bochner-vector}
Let $(X, \cm, \mu)$ be a measure space, $E, F$ be normed spaces over $K \in \RC$, $G$ be a Banach space over $K$,
\[
\lambda: E \times F \to G \quad (x, y) \mapsto xy
\]
be a bounded bilinear map, $\mu: \cm \to F$ be a vector measure, $\seq{f_n} \subset L^1(X, |\mu|; E)$, and $f \in L^1(X, |\mu|; E)$. If
\begin{enumerate}
\item[(a)] $f_n \to f$ strongly pointwise.
\item[(b)] There exists $g \in L^1(X) \cap L^+(X)$ such that $\norm{f_n}_E \le g$ for all $n \in \natp$.
\end{enumerate}
then $\int f d\lambda\mu = \limv{n}\int f_n d\lambda\mu$.
\end{theorem}
\begin{proof}
By the classical \hyperref[Dominated Convergence Theorem]{proposition:dct-lp}, $f_n \to f$ in $L^1(X, |\mu|; E)$. Since $h \mapsto \int h d\lambda\mu$ is a bounded linear operator, $\int f d\lambda\mu = \limv{n}\int f_n d\lambda\mu$.
\end{proof}