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Signed-off-by: zeramorphic <[email protected]>
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zeramorphic committed Jun 12, 2024
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3 changes: 1 addition & 2 deletions iii/lc/02_medium_large_cardinals.tex
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Expand Up @@ -217,7 +217,7 @@ \subsection{Weakly compact cardinals}

If \( 2^\lambda \geq \kappa \), there is a family of pairwise distinct elements \( (f_\alpha)_{\alpha < \kappa} \) of \( B_\lambda \) of length \( \kappa \).
Define a colouring \( c \) of \( \kappa \) as follows.
A pair \( \alpha, \beta \) is red if the truth value of \( \alpha < \beta \) is the same as the truth value of \( f_\alpha \leq_{\mathrm{lex}} f_\beta \).
A pair \( \alpha, \beta \) is red if the truth value of \( \alpha \leq \beta \) is the same as the truth value of \( f_\alpha \leq_{\mathrm{lex}} f_\beta \).
A pair is blue otherwise.
Let \( H \) be a monochromatic set for \( c \).
If \( H \) is red, then \( f_\alpha \) forms a \( \leq_{\mathrm{lex}} \)-increasing sequence of length \( \kappa \).
Expand Down Expand Up @@ -336,4 +336,3 @@ \subsection{Strongly compact cardinals}
This is a \( \kappa \)-complete filter on \( \kappa \).
If \( U \) extends \( F \) then \( U \) must be nonprincipal, so by the Keisler--Tarski theorem, \( F \) can be extended to a \( \kappa \)-complete nonprincipal ultrafilter on \( \kappa \) as required.
\end{proof}

2 changes: 1 addition & 1 deletion iii/lc/04_large_large_cardinals.tex
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Expand Up @@ -189,7 +189,7 @@ \subsection{The upper limit}
\begin{enumerate}
\item The combinatorial lemma was proven using \( \mathsf{AC} \), and it is not known whether the proof works without it.
\item To prove Kunen's lemma, we did not need that \( \lambda \) is inaccessible.
More explicitly, if \( j : \mathrm{V}_\alpha \to M \) is an elementary embedding with critical point \( \kappa \) such that \( \hat\alpha + 2 \leq \alpha \) (to guarantee that \( f \in \mathrm{V}_\alpha \)), then \( \mathrm{V}_{\hat\kappa + 1} \nsubseteq M \).
More explicitly, if \( j : \mathrm{V}_\alpha \to M \) is an elementary embedding with critical point \( \kappa \) such that \( \hat\kappa + 2 \leq \alpha \) (to guarantee that \( f \in \mathrm{V}_\alpha \)), then \( \mathrm{V}_{\hat\kappa + 1} \nsubseteq M \).
\end{enumerate}
\end{remark}
\begin{corollary}
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4 changes: 2 additions & 2 deletions iii/lc/main.tex
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Expand Up @@ -64,8 +64,8 @@ \section*{Diagram of large cardinal properties}
% SC -> strong on ES3 46--48, shows how to make strongly compact cardinals embedding cardinals

The `small large cardinals' are usually considered those cardinals consistent with \( \mathrm{V} = \mathrm{L} \), and such large cardinal properties are usually downwards absolute.
Note that \( L \) has no measurable cardinals.
Indeed, if \( \mathrm{V} = \mathrm{L} \) and \( U \) is a \( \kappa \)-complete nonprincipal ultrafilter on \( \kappa \), then the ultrapower embedding \( j_U : L \to M \) must map to an inner model strictly smaller than \( L \), but such an inner model cannot exist.
Note that \( \mathrm{L} \) has no measurable cardinals.
Indeed, if \( \mathrm{V} = \mathrm{L} \) and \( U \) is a \( \kappa \)-complete nonprincipal ultrafilter on \( \kappa \), then the ultrapower embedding \( j_U : \mathrm{L} \to M \) must map to an inner model strictly smaller than \( \mathrm{L} \), but such an inner model cannot exist.

There are certain large cardinals called \emph{Woodin cardinals} which sit between strong and strongly compact cardinals.
They represent another boundary between sizes of large cardinal axioms, just like measurable cardinals; smaller large cardinals are sometimes called `medium-sized large cardinals', and the others are called `large large cardinals'.
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