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Topic: Hereditary size notion proving consistency of ZF
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Posts: 2,665
Registered: 6/29/07
Hereditary size notion proving consistency of ZF
Posted: Jan 19, 2013 1:19 PM
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I think that ZF can be proved consistent relative to consistency of
the following theory defined in the same language of ZF with the
following axioms:

Define: Set(x) iff Exist y. x in y

[1] Extensionality: as in Z

[2] Comprehension: If phi is a formula in which x is not free, then
(Exist x. for all y. y in x iff Set(y) & phi) is an axiom.

[3] Pairing: (for all y. y in x -> y=a or y=b) -> Set(x)

[4] Size: [Set(x) & y < x & for all m e z (m << Uy)] -> Set(z)


y < x is defined as: Exist s,f: s subset_of x & f:s --> y & f is

y << x is defined as: y < x & (for all z in TC(y). z < x)

TC(y)=x iff [for all z. z in x iff (for all s. y subset_of s & s is
transitive -> z in s)]

Uy=x iff [for all z. z in x iff Exist k. k in y & z in k]


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