Added local L^p spaces.

This commit is contained in:
Bokuan Li
2026-06-30 14:13:58 -04:00
parent 98127388ec
commit 8090f060d3
2 changed files with 45 additions and 0 deletions

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\input{./duality.tex} \input{./duality.tex}
\input{./ui.tex} \input{./ui.tex}
\input{./seq.tex} \input{./seq.tex}
\input{./local.tex}

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src/fa/lp/local.tex Normal file
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\section{Locally Integrable Functions}
\label{section:locally-integrable}
\begin{definition}[Locally Integrable*]
\label{definition:locally-integrable}
Let $(X, \cm, \cf, \mu)$ be a \hyperref[scaffolded]{definition:measure-scaffold} measure space, $E$ be a normed vector space over $K \in \RC$, $f: X \to E$ be strongly measurable, and $p \in [1, \infty]$, then $f$ is \textbf{locally $p$-integrable} if for every $A \in \cf$, $\int_A \norm{f}_A^p d\mu < \infty$.
The set $\mathcal{L}^p_\cf(X, \cm, \mu; E) = \mathcal{L}^p_\cf(X; E) = \mathcal{L}^p_\cf(\mu; E)$ is the space of all locally $p$-integrable $E$-valued functions on $X$.
\end{definition}
\begin{definition}[Locally Bounded*]
\label{definition:locally-bounded-measure}
Let $(X, \cm, \cf, \mu)$ be a \hyperref[scaffolded]{definition:measure-scaffold} measure space, $E$ be a normed vectorr space over $K \in \RC$, and $f: X \to E$ be strongly measurable, then $f$ is \textbf{essentially bounded} if for every $A \in \cf$, $\norm{\one_A f}_{L^\infty(A; E)} < \infty$.
The set $\mathcal{L}^\infty_\cf(X, \cm, \mu; E) = \mathcal{L}^\infty_\cf(X; E) = \mathcal{L}^\infty_\cf(\mu; E)$ is the space of all locally bounded $E$-valued functions on $X$.
\end{definition}
\begin{definition}[Local $L^p$ Space*]
\label{definition:local-lp-space}
Let $(X, \cm, \cf, \mu)$ be a \hyperref[scaffolded]{definition:measure-scaffold} measure space, $E$ be a normed vector space over $K \in \RC$, and $p \in [1, \infty]$. For each $A \in \cf$ and $f \in \mathcal{L}^p_\cf(X, \cm, \mu; E)$, let $[f]_{L^p_A(X; \mu)} = \norm{\one_A f}_{L^p(X; \mu)}$, then the $[\cdot]_{L^p_A(X; \mu)}$ is a seminorm on \hyperref[$\mathcal{L}^p_\cf(X; E)$]{definition:locally-integrable}. The set
\[
L^p_\cf(X, \cm, \mu; E) = \mathcal{L}^p_\cf(X, \cm, \mu; E)/\bracs{f|f = 0\text{ a.e.}}
\]
equipped with the seminorms $\bracsn{[\cdot]_{L^p_A(X;\mu)}|A \in \cf}$ is a separated locally convex space, and the \textbf{local $L^p$ space} of $(X, \cm, \mu)$.
\end{definition}
\begin{lemma}
\label{lemma:gluing-local-lp}
Let $(X, \cm, \cf, \mu)$ be a \hyperref[scaffolded]{definition:measure-scaffold} localisable measure space, $E$ be a normed vector space over $K \in \RC$, $p \in [1, \infty]$, and $\bracsn{f_A}_{A \in \cf}$ such that:
\begin{enumerate}[label=(\alph*)]
\item For each $A \in \cf$, $f_A \in \mathcal{L}^p(A; E)$.
\item For each $A, B \in \cf$, $f_A|_{A \cap B} = f_B|_{A \cap B}$ almost everywhere.
\item $\bigcup_{A \in \cf}f_A(A)$ is a separable subset of $E$.
\end{enumerate}
then there exists a unique $f \in L^p_\cf(X; E)$ such that $f|_A = f_A$ for all $A \in \cf$.
\end{lemma}
\begin{proof}
By the \hyperref[gluing lemma for measurable functions]{lemma:gluing-measurable}.
\end{proof}