From 3a8db01be5c1443f07c5c54bd528b63896376fed Mon Sep 17 00:00:00 2001 From: Bokuan Li Date: Sun, 21 Jun 2026 21:58:14 -0400 Subject: [PATCH] Added uniform description for convergence in measure. --- src/measure/measurable-maps/in-measure.tex | 42 ++++++++-------------- 1 file changed, 14 insertions(+), 28 deletions(-) diff --git a/src/measure/measurable-maps/in-measure.tex b/src/measure/measurable-maps/in-measure.tex index ffd7a51..41e3a7d 100644 --- a/src/measure/measurable-maps/in-measure.tex +++ b/src/measure/measurable-maps/in-measure.tex @@ -88,35 +88,21 @@ forms a fundamental system of entourages for a uniformity. The uniformity induced by $\fB$ is the \textbf{uniform structure of local convergence in measure} on $\mathscr{M}(X; Y)$. \end{definition} +\begin{proof} + It is sufficient to check the conditions of \autoref{proposition:fundamental-entourage-criterion}: + \begin{enumerate} + \item[(FB1)] For each $\eps, \eps', \delta, \delta' > 0$ and $A, A' \in \cm$ with $\mu(A), \mu(A') < \infty$, + \[ + U(A \cup A', \delta \wedge \delta', \eps \wedge \eps') \subset U(A, \delta, \eps) \cap U(A', \delta', \eps') + \] + \item[(UB3)] For each $\eps, \delta > 0$, $A \in \cm$ with $\mu(A) < \infty$, and $f, g, h \in \mathscr{M}(X; Y)$, + \[ + \bracs{d(f, h) > \delta} \subset \bracs{d(f, g) > \delta} \cup \bracs{d(g, h) > \delta} + \] - - - - -\begin{definition}[Convergence in Measure] -\label{definition:convergence-in-measure} - Let $(X, \cm, \mu)$ be a measure space, $(Y, d)$ be a metric space, and $\fF$ be a filter of $(\cm, \cb_Y)$-measurable functions, and $f$ be a $(\cm, \cb_Y)$-measurable function, then $\fF \to f$ \textbf{in measure} if for each $\eps > 0$, - \[ - \lim_{g, \fF}\mu(\bracs{d(f, g) > \eps}) = 0 - \] - - and $\fF \to f$ \textbf{locally in measure} if $\fF \to f$ in measure on every set of finite measure. - - Alternatively, if $\net{f}$ is a net of $(\cm, \cb_Y)$-measurable functions, then $f_\alpha \to f$ \textbf{in measure} if for each $\eps > 0$, - \[ - \lim_{\alpha \in A}\mu(\bracs{d(f, f_\alpha) > \eps}) = 0 - \] - - and $f_\alpha \to f$ \textbf{locally in measure} if $f_\alpha \to f$ in measure on every set of finite measure. -\end{definition} - - -\begin{definition}[Cauchy in Measure] -\label{definition:cauchy-in-measure} - Let $(X, \cm, \mu)$ be a measure space, $(Y, d)$ be a metric space, and $\fF$ be a filter of $(\cm, \cb_Y)$-measurable functions, then $\fF$ is \textbf{Cauchy in measure} if for every $\eps, \delta > 0$, there exists $A \in \fF$ such that $\mu(\bracs{d(f, g) > \delta}) < \eps$ for all $f, g \in A$. - - Alternatively, if $\net{f}$ is a net of $(\cm, \cb_Y)$-measurable functions, then $\net{f}$ is \textbf{Cauchy in measure} if for every $\eps, \delta > 0$, there exists $\alpha_0 \in A$ such that for each $\alpha, \beta \in A$ with $\alpha, \beta \ge \alpha_0$, $\mu(\bracs{d(f_\alpha, f_\beta) > \delta}) < \eps$. -\end{definition} + so $U(A, \delta/2, \eps/2) \circ U(A, \delta/2, \eps/2) \subset U(A, \delta, \eps)$. + \end{enumerate} +\end{proof} \begin{proposition} \label{proposition:convergence-in-measure}