diff --git a/inputs/lecture_08.tex b/inputs/lecture_08.tex index 09efe3f..4288b7f 100644 --- a/inputs/lecture_08.tex +++ b/inputs/lecture_08.tex @@ -58,7 +58,7 @@ \end{proof} \subsection{Parametrizations} -\todo{choose better title} +%\todo{choose better title} Let $\Gamma$ denote a collection of sets in some space. @@ -109,9 +109,9 @@ where $X$ is a metrizable, usually second countable space. put $(y,x) \in \cU$ iff $x \in \bigcup \{V_n : y_n = 1\}$. $\cU$ is open. - Let $V = \bigcup \{V_n : V_n \subseteq V\}$. - Pick $y \in 2^\omega$ - and let $y_n = 1$ iff $V_n \subseteq V$. + For any $V \overset{\text{open}}{\subseteq} X$, + define $y \in 2^\omega$ + by $y_n = 1$ iff $V_n \subseteq V$. Then $\cU_y = V$. @@ -125,7 +125,7 @@ where $X$ is a metrizable, usually second countable space. Recall that $\eta_1 \le \eta_2 \implies \Pi^0_{\eta_1}(X) \subseteq \Pi^0_{\eta_2}(X)$. Note that if $A = \bigcup_n A_n$, with $A_n \in \Pi^0_{\eta_n}(X)$ - some $\eta_n < \xi$, + for some $\eta_n < \xi$, we also have $A = \bigcup_n A_n'$ with $A'_n \in \Pi^0_{\xi_n}(X)$. @@ -146,7 +146,7 @@ where $X$ is a metrizable, usually second countable space. Since $2^{\omega}$ embeds into any uncountable polish space $Y$ such that the image is closed, - we can $2^{\omega}$ by $Y$ + we can replace $2^{\omega}$ by $Y$ in the statement of the theorem.% \footnote{By definition of the subspace topology and transfinite induction, $\Sigma^0_\xi(Y)\defon{2^\omega} = \Sigma^0_\xi(2^\omega)$.}