Fraenkel \(\cal N40\): Howard/Rubin Model II | Back to this models page

Description: A variation of \(\cal N38\)

When the book was first being written, only the following form classes were known to be true in this model:

Form Howard-Rubin Number Statement
8

\(C(\aleph_{0},\infty)\):

14

BPI: Every Boolean algebra has a prime ideal.

23

\((\forall \alpha)(UT(\aleph_{\alpha},\aleph_{\alpha}, \aleph_{\alpha}))\): For every ordinal \(\alpha\), if \(A\) and every member of \(A\) has cardinality \(\aleph_{\alpha}\), then \(|\bigcup A| = \aleph _{\alpha }\).

43

\(DC(\omega)\) (DC), Principle of Dependent Choices: If \(S\)  is  a relation on a non-empty set \(A\) and \((\forall x\in A) (\exists y\in A)(x S y)\)  then there is a sequence \(a(0), a(1), a(2), \ldots\) of elements of \(A\) such that \((\forall n\in\omega)(a(n)\mathrel S a(n+1))\).  See Tarski [1948], p 96, Levy [1964], p. 136.

60

\(C(\infty,WO)\): Every set of non-empty, well orderable sets has a choice function.
Moore, G. [1982], p 125.

91

\(PW\):  The power set of a well ordered set can be well ordered.

113

Tychonoff's Compactness Theorem for Countably Many Spaces: The product of a countable set of compact spaces is compact.

130

\({\cal P}(\Bbb R)\) is well orderable.

165

\(C(WO,WO)\):  Every well ordered family of non-empty, well orderable sets has a choice function.

191

\(SVC\): There is a set \(S\) such that for every set \(a\), there is an ordinal \(\alpha\) and a function from \(S\times\alpha\) onto \(a\).

295

DO:  Every infinite set has a dense linear ordering.

305

There are \(2^{\aleph_0}\) Vitali equivalence classes. (Vitali equivalence classes are equivalence classes of the real numbers under the relation \(x\equiv y\leftrightarrow(\exists q\in{\Bbb Q})(x-y=q)\).). \ac{Kanovei} \cite{1991}.

317

Weak Sikorski Theorem:  If \(B\) is a complete, well orderable Boolean algebra and \(f\) is a homomorphism of the Boolean algebra \(A'\) into \(B\) where \(A'\) is a subalgebra of the Boolean algebra \(A\), then \(f\) can be extended to a homomorphism of \(A\) into \(B\).

345

Rasiowa-Sikorski Axiom:  If \((B,\land,\lor)\) is a Boolean algebra, \(a\) is a non-zero element of \(B\), and \(\{X_n: n\in\omega\}\) is a denumerable set of subsets of \(B\) then there is a maximal filter \(F\) of \(B\) such that \(a\in F\) and for each \(n\in\omega\), if \(X_n\subseteq F\) and \(\bigwedge X_n\) exists then \(\bigwedge X_n \in F\).

368

The set of all denumerable subsets of \(\Bbb R\) has power \(2^{\aleph_0}\).

369

If \(\Bbb R\) is partitioned into two sets, at least one of them has cardinality \(2^{\aleph_0}\).

When the book was first being written, only the following form classes were known to be false in this model:

Form Howard-Rubin Number Statement
3  \(2m = m\): For all infinite cardinals \(m\), \(2m = m\).
15

\(KW(\infty,\infty)\) (KW), The Kinna-Wagner Selection Principle: For every  set \(M\) there is a function \(f\) such that for all \(A\in M\), if \(|A|>1\) then \(\emptyset\neq f(A)\subsetneq A\). (See Form 81(\(n\)).  

40

\(C(WO,\infty)\):  Every well orderable set of non-empty sets has a choice function. Moore, G. [1982], p 325.

51

Cofinality Principle: Every linear ordering has a cofinal sub well ordering.  Sierpi\'nski [1918], p 117.

118

Every linearly orderable topological space is normal.  Birkhoff [1967], p 241.

144

Every set is almost well orderable.

152

\(D_{\aleph_{0}}\): Every non-well-orderable set is the union of a pairwise disjoint, well orderable family of denumerable sets.  (See note 27 for \(D_{\kappa}\), \(\kappa\) a well ordered cardinal.)

163

Every non-well-orderable set has an infinite, Dedekind finite subset.

181

\(C(2^{\aleph_0},\infty)\): Every set \(X\) of non-empty sets such that \(|X|=2^{\aleph_0}\) has a choice function.

192

\(EP\) sets: For every set \(A\) there is a projective set \(X\) and a function from \(X\) onto \(A\).

193

\(EFP\ Ab\): Every Abelian group is a homomorphic image of a free projective Abelian group.

253

\L o\'s' Theorem: If \(M=\langle A,R_j\rangle_{j\in J}\) is a relational system, \(X\) any set and \({\cal F}\) an ultrafilter in \({\cal P}(X)\), then \(M\) and \(M^{X}/{\cal F}\) are elementarily equivalent.

328

\(MC(WO,\infty)\): For  every well ordered set \(X\) such that for all \(x\in X\), \(|x|\ge 1\), there is a function \(f\) such that and for every \(x\in X\), \(f(x)\) is a finite, non-empty subset of \(x\). (See Form 67.)

Historical background: \(A\) and\(\cal G\) are the same as in \(\cal N38\), but \(S\) is the set of all subsetsof \(A\) that satisfy conditions (b) and (c) in the definition of \(S\) in\(\cal N38\). Thus, we no longer require supports to be well ordered by\(\le\). \(\cal N40\) has many of the same properties as \(\cal N38\), BPI (14)and \(C(\aleph_0,\infty)\) (8) are true, but \(C(2^{\aleph_0}, \infty)\) (181)and the \(2m=m\) principle (3) are false. (See Note 104.)Form 113(Tychonoff's Compactness Theorem for countably many spaces) is true herealso, because 14 + 8 implies 113. However, in this model, the Principle ofDependent Choices (43) is true. See Howard/Rubin [1996] forproofs. Using the fact that the Kinna-Wagner Selection Principle (15) isfalse and the Ordering Principle (30) is true (14 implies 30), Kromproves that there is an ordered topological space that is not normal (118is false). Since 8 is true, it follows from Brunner [1982a] thatin this model there is a set that cannot be well ordered and does not havean infinite Dedekind finite subset, (163 is false). (Form 8 plusForm 163iff AC.)Form 14 implies 49 (Every partial ordering can be extended to alinear ordering.) and 49 + 51 (Every linear ordering has a cofinal subwell ordering.) iff AC. (See Morris [1969] and Note 121.) Thus,form 51 is false. Blass [1979] has shown that 191 (There is aset \(X\) such that for each set \(a\) there is an ordinal \(\alpha\) and afunction \(f\) mapping \(X\times\alpha\) onto \(a\).) is true in everypermutation model with a set of atoms. He has also shown that 8 + 191 +193 (Every Abelian group is a homomorphic image of a free projectiveAbelian group.) iff AC. Thus, 193 is false. (See Note 60 for definitions.)SinceForm 14 impliesForm 30 (Ordering Principle) andForm 43 impliesform 296 (Every infinite set is the disjoint union of infinitely manyinfinite sets.), it follows from Pincus [1997] thatForm 295(Every infinite set has a dense linear ordering.) is true. Form 14implies 62 (\(C(\infty,<\aleph_0)\)) and Howard [1973] has shownthat in every FM model, 62 implies 60 (\(C(\infty, WO)\)). Thus, 60 is true.Moreover, in every FM model, 60 + 40 (\(C(WO, \infty)\)) implies AC, so 40is false. (See Howard/Rubin [1995b].) It is also shown inHoward [1973] that in every FM model 14 implies the WeakSikorski Theorem (317), so 317 is true.Form 40 is false andForm 122(\(C(WO,<\infty)\)) is true because 60 implies 122. Therefore,Form 328(\(MC(WO,\infty)\)) is false because \(122 + 328\to 40\). Since 43 + 14 isequivalent to 345 ([345 A]),Form 345 is true.

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