[FOM] What is second order ZFC?
MartDowd at aol.com
MartDowd at aol.com
Tue Sep 3 11:34:27 EDT 2013
Harvey,
I found this question confusing, but it prompted me to consider V=L and
second order set theory. Suppose at stage alpha one adds the subsets which
are second order definable. Call the result L_2. Clearly L\subseteq
L_2\subseteq V, so if V=L all three are equal. Obvious questions include the
following.
Is L_2 a model of ZFC (i'm pretty sure it is)
Is it consistent that L_2=neq V? (I think the generic model over L_2 by a
Cohen real shows that it is)
Is L_2=L? (I couldn't see an obvious proof)
What kind of sets might be in L_2-L?
Is CH true in L_2?
- Martin Dowd
In a message dated 9/2/2013 9:00:06 A.M. Pacific Daylight Time,
hmflogic at gmail.com writes:
I will jump start the ensuing discussion by asking these questions:
1. Is CH an axiom of ZFC?
2. Is CH an "axiom" of second order ZFC"?
3. Is CH a theorem of ZFC?
4. Is CH an "axiom of second order ZFC"?
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