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Signed-off-by: zeramorphic <[email protected]>
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zeramorphic committed May 16, 2024
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8 changes: 4 additions & 4 deletions iii/forcing/02_constructibility.tex
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Expand Up @@ -121,7 +121,7 @@ \subsection{G\"odel functions}
\begin{remark}
\begin{enumerate}
\item The reversed order of the free variables is done purely for technical reasons.
\item \( \mathcal F_2 \) will correspond to disjunction for \( \Delta_0 \) formulas, intersection will correspond to intersection, \( \mathcal F_3 \) will give negation, and \( \mathcal F_9 \) and \( \mathcal F_{10} \) will give atomic formulas.
\item \( \mathcal F_2 \) will correspond to disjunction for \( \Delta_0 \) formulas, intersection will correspond to conjunction, \( \mathcal F_3 \) will give negation, and \( \mathcal F_9 \) and \( \mathcal F_{10} \) will give atomic formulas.
\item \( \mathcal F_7 \) and \( \mathcal F_8 \) will deal with ordered \( n \)-tuples.
For example, the triple \( \langle x_1, x_2, x_3 \rangle \) is formed using \( x_1 \) and \( \langle x_2, x_3 \rangle \), but it cannot be formed using \( \langle x_1, x_2 \rangle \) and \( x_3 \) without \( \mathcal F_7 \) or \( \mathcal F_8 \).
\end{enumerate}
Expand Down Expand Up @@ -406,7 +406,7 @@ \subsection{Well-ordering the universe}
\item if \( x \in \mathrm{L}_\alpha \) and \( y \in \mathrm{L}_\beta \setminus \mathrm{L}_\alpha \), then \( x <_\beta y \).
\end{enumerate}
For limit cases, we take unions:
\[ <_\gamma = \bigcup_{\alpha < \gamma} <_\gamma \]
\[ {<_\gamma} = \bigcup_{\alpha < \gamma} <_\gamma \]
We now describe the construction of \( <_{\alpha + 1} \).
To do this, we consider the ordering on \( \mathrm{L}_\alpha \), and append the singleton \( \qty{\mathrm{L}_\alpha} \).
We then follow that by the elements of \( \mathcal D(\mathrm{L}_\alpha \cup \qty{\mathrm{L}_\alpha}) \setminus (\mathrm{L}_\alpha \cup \qty{\mathrm{L}_\alpha}) \).
Expand All @@ -417,7 +417,7 @@ \subsection{Well-ordering the universe}
\item Suppose that \( <_{\alpha + 1}^n \) is defined.
We end-extend \( <_{\alpha + 1}^n \) to form \( <_{\alpha + 1}^{n + 1} \) as follows.
Suppose \( x, y \notin \mathcal D^n(\mathrm{L}_\alpha \cup \qty{\mathrm{L}_\alpha}) \).
We say \( x <_{\alpha + 1}^{n+1} \) if either
We say \( x <_{\alpha + 1}^{n+1} y \) if either
\begin{enumerate}
\item the least \( i \leq 10 \) such that \( \exists u, v \in \mathcal D^n(\mathrm{L}_\alpha \cup \qty{\mathrm{L}_\alpha}) \) with \( x = \mathcal F_i(u, v) \) is less than the least \( i \leq 10 \) such that \( \exists u, v \in \mathcal D^n(\mathrm{L}_\alpha \cup \qty{\mathrm{L}_\alpha}) \) with \( y = \mathcal F_i(u, v) \); or
\item these indices \( i \) are equal, and the \( <_{\alpha + 1}^n \)-least \( u \in \mathcal D^n(\mathrm{L}_\alpha \cup \qty{\mathrm{L}_\alpha}) \) such that there exists \( v \in \mathcal D^n(\mathrm{L}_\alpha \cup \qty{\mathrm{L}_\alpha}) \) with \( x = \mathcal F_i(u, v) \) is less than the \( <_{\alpha + 1}^n \)-least \( u \in \mathcal D^n(\mathrm{L}_\alpha \cup \qty{\mathrm{L}_\alpha}) \) such that there exists \( v \in \mathcal D^n(\mathrm{L}_\alpha \cup \qty{\mathrm{L}_\alpha}) \) with \( y = \mathcal F_i(u, v) \); or
Expand All @@ -438,7 +438,7 @@ \subsection{The generalised continuum hypothesis in \texorpdfstring{\( \mathrm{L
\begin{enumerate}
\item For all \( n \in \omega \), we have \( \mathrm{L}_n = \mathrm{V}_n \).
\item If \( M \) is infinite, then \( \abs{M} = \abs{\operatorname{Def}(M)} \).
\item If \( \alpha \) is an ordinal, then \( \abs{\mathrm{L}_\alpha} = \abs{\alpha} \).
\item If \( \alpha \) is an infinite ordinal, then \( \abs{\mathrm{L}_\alpha} = \abs{\alpha} \).
\end{enumerate}
\end{lemma}
\begin{lemma}[G\"odel's condensation lemma]
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2 changes: 1 addition & 1 deletion iii/forcing/03_forcing.tex
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Expand Up @@ -643,7 +643,7 @@ \subsection{The forcing theorem}
\begin{corollary}
Suppose that \( M \) is a countable transitive model of \( \mathsf{ZF} \), \( \mathbb P \in M \) is a forcing poset, and \( \varphi(u) \) is a formula.
Then for any name \( \dot x \in M^{\mathbb P} \),
\[ (p \Vdash \varphi(\dot x))^M \leftrightarrow \text{for any \( \mathbb P \)-generic filter \( G \) with \( p \in G \), } M[G] \Vdash \varphi(\dot x^G) \]
\[ (p \Vdash \varphi(\dot x))^M \leftrightarrow \text{for any \( \mathbb P \)-generic filter \( G \) with \( p \in G \), } M[G] \vDash \varphi(\dot x^G) \]
\end{corollary}
The only reason we need countability is so that every condition is contained in a generic filter.
\begin{proof}
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2 changes: 1 addition & 1 deletion iii/lc/03_reflection.tex
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Expand Up @@ -402,7 +402,7 @@ \subsection{The fundamental theorem on measurable cardinals}
Let \( \gamma < \kappa \), and fix \( (A_\alpha)_{\alpha < \gamma} \) such that \( A_\alpha \in U \) for each \( \alpha < \gamma \).
Then \( \kappa \in j(A_\alpha) \) for all \( \alpha < \gamma \).
Then \( \bigcap_{\alpha < \gamma} A_\alpha \in U \) if and only if \( \kappa \in j\qty(\bigcap_{\alpha < \gamma} A_\alpha) \).
Note that being an element of \( \bigcap_{\alpha < \gamma} A_\gamma \) is a formula that says that \( \vb A \) is a sequence of objects \( A_\alpha \), the \( \alpha \)th element of this sequqence is \( A_\alpha \), and \( \beta \) is an element of each element of the sequence.
Note that being an element of \( \bigcap_{\alpha < \gamma} A_\gamma \) is a formula that says that \( \vb A \) is a sequence of objects \( A_\alpha \), the \( \alpha \)th element of this sequence is \( A_\alpha \), and \( \beta \) is an element of each element of the sequence.
Therefore \( \beta \in j\qty(\bigcap_{\alpha < \gamma} A_\alpha) \) if and only if \( \beta \) is an element of all elements of the sequence \( j(\vb A) \).
Clearly, \( j(\vb A) \) is a sequence of subsets of \( j(\kappa) \) of length \( j(\gamma) = \gamma \).
Since \( A_\alpha \) is the \( \alpha \)th element of \( \vb A \), \( j(A_\alpha) \) is the \( j(\alpha) \)th element of \( j(\vb A) \), but \( j(\alpha) = \alpha \).
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2 changes: 1 addition & 1 deletion iii/mtncl/02_quantifier_elimination.tex
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Expand Up @@ -58,7 +58,7 @@ \subsection{Skolem functions}

\subsection{Skolemisation theorem}
\begin{theorem}
Every first-order language \( \mathcal L \) can be expanded to some \( \mathcal L^+ \supseteq \mathcal L \) that includes an \( \mathcal L^+ \)-theory \( \Sigma \) such that
Every first-order language \( \mathcal L \) can be expanded to some \( \mathcal L^+ \supseteq \mathcal L \) that admits an \( \mathcal L^+ \)-theory \( \Sigma \) such that
\begin{enumerate}
\item \( \Sigma \) is a Skolem \( \mathcal L^+ \)-theory;
\item any \( \mathcal L \)-structure can be expanded to an \( \mathcal L^+ \)-structure that models \( \Sigma \); and
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