*EDIT: Joel's answer shows that no $\Sigma\_2$ large cardinal property will do the job - however, $\Pi\_2$ properties (such as [unfoldability](https://en.wikipedia.org/wiki/Unfoldable_cardinal) and its relatives) may still be useful.*




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*Throughout this question, I'm working in "$V=L$". So when I say "large cardinal," I mean "**small** large cardinal".*


Informally, I want to ask: How much of the "$L$-theory" of a cardinal does a large cardinal property imply? That is, if I know that $\alpha$ and $\beta$ both have some large cardinal property $(\*)$, what sorts of (not necessarily first-order) sentences do I know that $L\_\alpha$ and $L\_\beta$ agree about?


Formally, fix an ordinal $\gamma$. Say that a large cardinal property $(\*)$ is "$\gamma$-decisive" if whenever $\alpha, \beta$ have property $(\*)$, we have $$L\_{\alpha+\gamma}\equiv L\_{\beta+\gamma}.$$ My question is:



> 
> What are some examples of $\gamma$-decisive large cardinal properties?
> 
> 
> 


(CAVEAT: Obviously *any* large cardinal property can be arbitrarily decisive: suppose it has no instances, or exactly one! So really I want to know about large cardinal properties whose decisiveness can be *proved* in ZFC+V=L, or some strengthening thereof that does not limit the number of relevant large cardinals.)


Note that decisiveness looks a lot (at least to me) like indescribability; however, indescribability doesn't quite seem to do the job, unless I'm missing something.




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I'm also interested in decisiveness *with parameters* - e.g. for a finite tuple of sets $\overline{c}\in L$, say that a large cardinal property $(\*)$ is $\gamma$-decisive over $\overline{c}$ if whenever $\alpha,\beta$ have property $(\*)$ with $\overline{c}\in L\_\alpha\cap L\_\beta$, we have $$(L\_\alpha, \overline{c})\equiv(L\_\beta,\overline{c}).$$ But understanding the parameter-free version should come first, and besides, I imagine the situations aren't too different. 


By contrast, something potentially interesting happens if we allow, not tuples of *elements of $L$*, but tuples $\overline{C}$ of *subsets of $L$* which are in $V$ but not necessarily $L$ - coded as unary predicates, of course. A really overkill example of this would be the $0^\#$ as a unary predicate, but already tamer examples could be interesting. For instance, suppose $\overline{C}$ is a finite sequence of mutually Cohen reals over $L$ - then what are some $\gamma$-decisive *over $\overline{C}$* large cardinal properties? But this question seems much broader, and much harder, so I'll merely mention it as a curiosity. (Note that in this context, detrivializing things becomes a bit trickier, so this is a more informal question.)



How similar are large cardinals, over $L$?
**Updated answer**. I claim that none of the familiar large cardinal
notions consistent with $V=L$ are provably $\gamma$-decisive for
any $\gamma$. This includes the cases of wordly cardinals,
inaccessible cardinals, uplifting cardinals, Mahlo cardinals weakly
compact cardinals, $\Pi^n\_m$-indescribable cardinals, totally
indescribable cardinals, unfoldable cardinals and all the others.


First, as a warm-up, let's handle the case of $\Sigma\_2$-definable
large cardinal notions.


**Theorem.** If a large cardinal notion LC is $\Sigma\_2$-definable
and there are a proper class of them in $L$, then there is no
$\gamma$ for which they are $\gamma$-decisive.


**Proof.** To see this, fix any $\gamma$, and let $\kappa$ be the
least LC cardinal above $\gamma$. Note that both $\kappa$ and
$\gamma$ are definable in $L\_{\kappa+\gamma}$, since $\kappa$ is
the largest cardinal of this structure, and $\gamma$ is least such
that $\kappa+\gamma$ does not exist. Further, since $\kappa$ was
the least LC cardinal above $\gamma$, it follows that
$L\_{\kappa+\gamma}$ will agree that there are no such large
cardinals of that type in the interval $(\gamma,\kappa)$, since
$\Sigma\_2$ definitions express locally verifiable properties (see
my blog post about [Local properties in set
theory](http://jdh.hamkins.org/local-properties-in-set-theory/)).
But the corresponding fact will not be true in $L\_{\delta+\gamma}$
for some other much larger LC cardinal $\delta$, since once
$\delta$ is large enough, then $L\_{\delta+\gamma}$ will think that
$\kappa$ is an LC cardinal. So $L\_{\kappa+\gamma}$ is not
elementarily equivalent to all $L\_{\delta+\gamma}$, and so the LC
large cardinal notion is not $\gamma$-decisive in this situation.
**QED**


Next, with a slightly stronger assumption on consistency, we can
handle the $\Pi\_2$-definable notions.


**Theorem.** Assume that a large cardinal notion LC is
$\Pi\_2$-definable and there are a sufficiently stationary proper
class of them in $L$, then there is no $\gamma$ for which they are
$\gamma$-decisive.


**Proof.** Fix any $\gamma$, and assume that the class of LC
cardinals in $L$ meets every $\Pi\_2$-definable class club. Let
$C$ be the club of $\Sigma\_2$-correct cardinals $\delta$, those for
which $V\_\delta\prec\_{\Sigma\_2} V$. This is $\Pi\_2$-definable. Let
$\kappa$ be the least LC cardinal in $C$ above $\gamma$. Note that
both $\kappa$ and $\gamma$ are definable in $L\_{\kappa+\gamma}$.
Further, since $\kappa$ is $\Sigma\_2$-correct, it must be a
beth-fixed-point, and so $L\_\kappa=(V\_\kappa)^L$. Since $L\_\kappa$
is $\Sigma\_2$-correct and hence also $\Pi\_2$-correct, it is correct
about the LC cardinals below $\kappa$. And it is also correct about
the $\Sigma\_2$-cardinals below $\kappa$. So by the minimality of
$\kappa$, the structure $L\_\kappa$ can see that there is no
$\Sigma\_2$-correct LC cardinal below $\kappa$ and above $\gamma$,
and this is part of the theory of $L\_{\kappa+\gamma}$. But now, if
$\delta$ is a larger LC cardinal in $C$, then $L\_{\delta+\gamma}$
will be able to see that there is a $\Sigma\_2$-correct LC cardinal
below $\delta$. And so $L\_{\kappa+\gamma}$ and $L\_{\delta+\gamma}$
do not have the same theory. So the LC cardinals are not
$\gamma$-decisive. **QED**


Finally, we can use this idea to push through an argument for any
first-order definable large cardinal notion.


**Theorem.** No first-order definable large cardinal notion LC is
provably $\gamma$-decisive for any $\gamma$, if it is consistent
that there is a stationary proper class of LC cardinals in $L$.


**Proof.** Suppose that the LC large cardinal notion is
$\Sigma\_n$-definable, and the class of LC cardinals in $L$ is
stationary with respect to all $\Pi\_n$-definable class clubs. Fix
any $\gamma$, and let $\kappa$ be the least $\Sigma\_n$-correct LC
cardinal above $\gamma$. There is such a $\kappa$ because the class
of $\Sigma\_n$-correct ordinals is a $\Pi\_n$-definable class club.
Both $\kappa$ and $\gamma$ are definable in $L\_{\kappa+\gamma}$,
and $L\_\kappa$ is correct about LC cardinals and about
$\Sigma\_n$-correctness. So $L\_\kappa$ will see no
$\Sigma\_n$-correct LC cardinals above $\gamma$. But if we use a
much larger $\Sigma\_n$-correct LC cardinal $\delta$, then
$L\_\delta$ will see that $\kappa$ is a $\Sigma\_n$-correct LC
cardinal above $\gamma$. So $L\_{\kappa+\gamma}$ and
$L\_{\delta+\gamma}$ will have different theories. **QED**


