diff --git a/src/measure/measure/localisable.tex b/src/measure/measure/localisable.tex index 5712aaf..7bfb207 100644 --- a/src/measure/measure/localisable.tex +++ b/src/measure/measure/localisable.tex @@ -153,11 +153,13 @@ \item For each $y \in Y$, $f^{-1}(y) = P(y)$, so $f \in \mathcal{L}^0(X; Y)$ is measurable. \item Let $A \in \cf$, then for each $y \in Y$, $\mu(f_A^{-1}(y) \setminus P(y)) = 0$. On the other hand, \begin{align*} - (P(y) \cap A) \setminus f_A^{-1}(y) &= P(y) \cap \bigcup_{z \in Y \setminus \bracs{y}}f_A^{-1}(z) \\ - &\subset \braks{P(y) \cap \bigcup_{z \in Y \setminus \bracs{y}}P(z)} \cup \bigcup_{z \in Y \setminus \bracs{y}}f_A^{-1}(z) \setminus P(z) + \mu\braks{(P(y) \cap A) \setminus f_A^{-1}(y)} &\le \sum_{z \in Y \setminus \bracs{y}}\mu(P(y) \cap f_A^{-1}(z) ) \\ + &\le \sum_{z \in Y \setminus \bracs{y}}\mu(P(y) \cap P(z)) \\ + &+ \sum_{z \in Y \setminus \bracs{y}}\mu(f_A^{-1}(z) \setminus P(z)) \\ + &= 0 \end{align*} - - is a null set. Therefore $f|_A = f_A$ almost everywhere. + + so $f|_A = f_A$ almost everywhere on $A$. \item[(U)] For all $A \in \cf$, $f|_A = g|_A$ almost everywhere. Since $\mu$ is semifinite, $f = g$ almost everywhere. \end{enumerate} @@ -182,12 +184,14 @@ \item For each $A \in \cf$, $f_n|_A = f_{A, n}$ almost everywhere. \end{enumerate} - Since $Y$ is Polish, \autoref{proposition:metric-measurable-limit} implies that $\bracsn{\limv{n}f_n \text{ exists}} \in \cm$. For each $A \in \cf$, since $f_n|_A = f_{A, n}$ almost everywhere, $\limv{n}f_{A, n}$ and $\limv{n}f_{n}|_A$ exist and are equal almost everywhere on $A$. Thus - \[ - \mu\paren{\bracs{\limv{n}f_n \text{ does not exist}} \cap A} \le \mu\bracs{\limv{n}f_{A, n} \text{ does not exist}} + 0 = 0 - \] + Since $Y$ is Polish, \autoref{proposition:metric-measurable-limit} implies that $\bracsn{\limv{n}f_n \text{ exists}} \in \cm$. For each $A \in \cf$, $f_{A, n} \to f_n$ pointwise by (i). For each$n \in \natp$, $f_{A, n} = f_n|_A$ almost everywhere on $A$ by (2). Thus + \begin{align*} + \bracs{\limv{n}f_n \text{ exists}} \cap A &\subset \bigcap_{n \in \natp}\bracs{f_{A, n} = f_n|_A} \\ + \mu\paren{\bracs{\limv{n}f_n \text{ exists}} \cap A} &= \mu\paren{\bigcap_{n \in \natp}\bracs{f_{A, n} = f_n|_{A}}} = \mu(A) \\ + \mu\paren{\bracs{\limv{n}f_n \text{ does not exist}} \cap A} &= 0 + \end{align*} - As $\mu$ is semifinite, $\mu\bracsn{\limv{n}f_n \text{ does not exist}} = 0$, so there exists $f \in \mathcal{L}^0(X; Y)$ such that $f = \limv{n}f_n$ almost everywhere. In which case, + As $\mu$ is semifinite, $\mu\bracsn{\limv{n}f_n \text{ does not exist}} = 0$. By (1) and \autoref{proposition:metric-measurable-limit}, there exists $f \in \mathcal{L}^0(X; Y)$ such that $f = \limv{n}f_n$ almost everywhere. In which case, \begin{enumerate} \item $f \in \mathcal{L}^0(X; Y)$. \item For each $A \in \cf$, $f|_A = \limv{n}f_n|_A = \limv{n}f_{A, n} = f_A$ almost everywhere.