Skip to content

Commit

Permalink
Fix typo
Browse files Browse the repository at this point in the history
Signed-off-by: zeramorphic <[email protected]>
  • Loading branch information
zeramorphic committed Mar 13, 2024
1 parent 574e8ad commit 677cbb2
Show file tree
Hide file tree
Showing 2 changed files with 4 additions and 4 deletions.
2 changes: 1 addition & 1 deletion iii/forcing/04_forcing_and_independence.tex
Original file line number Diff line number Diff line change
Expand Up @@ -561,7 +561,7 @@ \subsection{The mixing lemma}
For example, in \( p \Vdash \exists x.\, (\dot a \in x \wedge \dot b \in x) \), we can find a name \( \dot x = \operatorname{op}(\dot a, \dot b) \) without needing to know \( G \).
Informally, the mixing lemma says that this is always the case, as long as \( M \) has \( \mathsf{AC} \).
\begin{theorem}[the mixing lemma]
(\mathsf{ZFC})
(\( \mathsf{ZFC} \))
Suppose that \( (p \Vdash \exists x.\, \varphi(x))^M \).
Then there is a name \( \dot x \in M^{\mathbb P} \) such that \( (p \Vdash \varphi(\dot x))^M \).
\end{theorem}
Expand Down
6 changes: 3 additions & 3 deletions iii/lc/02_measurable_cardinals.tex
Original file line number Diff line number Diff line change
Expand Up @@ -545,7 +545,7 @@ \subsection{Ultrapowers of the universe}
(c_\alpha) < (\id_\kappa) &\leftrightarrow \qty{\gamma \mid c_\alpha(\gamma) < \id_\kappa(\gamma)} \in U \\
&\leftrightarrow \qty{\gamma \mid \alpha < \gamma} \in U
\end{align*}
But by a size argument, \( \qty{\gamma \mid \gamma \leq \alpha} \notin U \) as \( U \) is nonprincipal, so we must have \( \alpha < (id) \).
But by a size argument, \( \qty{\gamma \mid \gamma \leq \alpha} \notin U \) as \( U \) is nonprincipal, so we must have \( \alpha < (\id) \).
Also,
\begin{align*}
(\id_\kappa) < (c_\kappa) &\leftrightarrow \qty{\gamma \mid \id_\kappa(\gamma) < c_\kappa(\gamma)} \in U \\
Expand Down Expand Up @@ -795,7 +795,7 @@ \subsection{The fundamental theorem on measurable cardinals}
\end{proposition}
This proposition provides an alternative view of reflection.
Suppose that the ultrafilter \( U \) on \( \kappa \) is normal.
If \( M \vDash \Phi(\kappa) \), then \( M \vDash \Phi((id)) \).
If \( M \vDash \Phi(\kappa) \), then \( M \vDash \Phi((\id)) \).
By \L{}o\'s' theorem,
\[ \qty{\alpha < \kappa \mid \Phi(\id(\alpha))} \in U \]
So \( \Phi \) reflects not only on a set of size \( \kappa \), but on an ultrafilter set.
Expand All @@ -815,7 +815,7 @@ \subsection{The fundamental theorem on measurable cardinals}
\end{cases} \]
Thus the set of \( \alpha \) such that \( f(\alpha) \) is an \( \alpha \)-complete nonprincipal ultrafilter on \( \alpha \) is \( C \), so in \( U \).
Equivalently, the set of \( \alpha \) such that \( f(\alpha) \) is an \( \id(\alpha) \)-complete nonprincipal ultrafilter on \( \id(\alpha) \) is in \( U \).
So by \L{}o\'s' theorem, \( M \) believes that \( (f) \) is an \( (id) \)-complete nonprincipal ultrafilter on \( (id) \).
So by \L{}o\'s' theorem, \( M \) believes that \( (f) \) is an \( (\id) \)-complete nonprincipal ultrafilter on \( (\id) \).
So \( (f) \) witnesses that \( \kappa \) is measurable in \( M \).
\end{proof}
This shows that whether a cardinal \( \kappa \) is surviving depends only on \( \mathrm{V}_{\kappa + 2} \), and is therefore a 2-stable property.
Expand Down

0 comments on commit 677cbb2

Please sign in to comment.