fixed some typos; currying
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5 changed files with 16 additions and 16 deletions
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@ -185,11 +185,11 @@ suffices to show that open balls in one metric are unions of open balls in the o
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\begin{definition}[Our favourite Polish spaces]
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\leavevmode
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\begin{itemize}
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\item $2^{\omega}$ is called the \vocab{Cantor set}.
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\item $2^{\N}$ is called the \vocab{Cantor set}.
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(Consider $2$ with the discrete topology)
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\item $\omega^{\omega}$ is called the \vocab{Baire space}.
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($\omega$ with descrete topology)
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\item $[0,1]^{\omega}$ is called the \vocab{Hilbert cube}.
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\item $\cN \coloneqq \N^{\N}$ is called the \vocab{Baire space}.
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($\N$ with descrete topology)
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\item $\mathbb{H} \coloneqq [0,1]^{\N}$ is called the \vocab{Hilbert cube}.
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($[0,1] \subseteq \R$ with the usual topology)
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\end{itemize}
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\end{definition}
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@ -78,18 +78,17 @@ where $X$ is a metrizable, usually second countable space.
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we also have
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$A = \bigcup_n A_n'$ with $A'_n \in \Pi^0_{\xi_n}(X)$.
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We construct a $(2^\omega)^\omega \cong 2^\omega$-universal set
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We construct a $(2^{\omega \times \omega}) \cong 2^\omega$-universal set
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for $\Sigma^0_\xi(X)$.
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For $(y_n) \in (2^\omega)^\omega$
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For $(y_{m,n}) \in (2^{\omega \times \omega})$
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and $x \in X$
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we set $((y_n), x) \in \cU$
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iff $\exists n.~(y_n, x) \in U_{\xi_n}$,
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i.e.~iff $\exists n.~x \in (U_{\xi_n})_{y_n}$.
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we set $((y_{m,n}), x) \in \cU$
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iff $\exists n.~((y_{m,n})_{m < \omega}, x) \in U_{\xi_n}$,
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i.e.~iff $\exists n.~x \in (U_{\xi_n})_{(y_{m,n})_{m < \omega}}$.
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Let $A \in \Sigma^0_\xi(X)$.
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Then $A = \bigcup_{n} B_n$ for some $B_n \in \Pi^0_{\xi_n}(X)$.
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% TODO
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Furthermore $\cU \in \Sigma^0_{\xi}((2^\omega)^\omega \times X)$.
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Furthermore $\cU \in \Sigma^0_{\xi}((2^{\omega \times \omega} \times X)$.
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\end{proof}
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\begin{remark}
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Since $2^{\omega}$ embeds
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@ -34,7 +34,8 @@ we need the following definition:
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\begin{lemma}
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\label{lem:lusinsephelp}
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If $P = \bigcup_{m < \omega} P_m$, $Q = \bigcup_{n < \omega} Q_n$ are such that
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for any $m, n$ the sets $P_m$ and $Q_n$ are Borel separable.
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for any $m, n$ the sets $P_m$ and $Q_n$ are Borel separable,
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then $P$ and $Q$ are Borel separable.
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\end{lemma}
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\begin{proof}
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For all $m, n$ pick $R_{m,n}$ Borel,
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@ -42,7 +43,7 @@ we need the following definition:
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and $Q_n \cap R_{m,n} = \emptyset$.
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Then $R = \bigcup_m \bigcap_n R_{m,n}$
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has the desired property
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that $R \subseteq R$ and $R \cap Q = \emptyset$.
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that $P \subseteq R$ and $R \cap Q = \emptyset$.
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\end{proof}
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\begin{notation}
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@ -60,7 +61,7 @@ we need the following definition:
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Write $A_s \coloneqq f(\cN_s)$ and $B_s \coloneqq g(\cN_s)$.
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Note that $A_s = \bigcup_m A_{s\concat m}$
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and $B_ns = \bigcup_{n < \omega} B_{s\concat n}$.
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and $B_s = \bigcup_{n < \omega} B_{s\concat n}$.
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In particular
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$A = \bigcup_{m < \omega} A_{\underbrace{\langle m \rangle}_{\in \omega^1}}$
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@ -183,7 +183,7 @@ i.e.}{}
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Let $X$ be Polish and $C \subseteq X$ coanalytic.
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Then $\phi\colon C \to \Ord$
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is a \vocab[Rank!$\Pi^1_1$-rank]{$\Pi^1_1$-rank}
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provided that $\le^\ast$ and $<^\ast$ are coanalytic subsets of $X \times X$,
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provided that $\le^\ast_\phi$ and $<^\ast_\phi$ are coanalytic subsets of $X \times X$,
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where
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$x \le^\ast_{\phi} y$
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iff
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@ -55,7 +55,7 @@
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then $\xi = \alpha$
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and
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\[
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E_\xi = E_\alpha = \bigcup_{\eta < \alpha}
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E_\xi = E_\alpha = \bigcup_{\eta < \alpha} E_\eta
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\]
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is a countable union of Borel sets by the previous case.
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\end{itemize}
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