Fraenkel \(\cal N15\): Brunner/Howard Model I | Back to this models page

Description: \(A=\{a_{i,\alpha}: i\in\omega\wedge\alpha\in\omega_1\}\)

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

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

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.

63

\(SPI\): Weak ultrafilter principle: Every infinite set has a non-trivial ultrafilter.
Jech [1973b], p 172 prob 8.5.

91

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

122

\(C(WO,<\aleph_{0})\): Every well ordered set of non-empty finite sets has a choice function.

130

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

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.)

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 \(a\).

273

There is a subset of \({\Bbb R}\) which is not Borel.

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}.

309

The Banach-Tarski Paradox: There are three finite partitions \(\{P_1,\ldots\), \(P_n\}\), \(\{Q_1,\ldots,Q_r\}\) and \(\{S_1,\ldots,S_n, T_1,\ldots,T_r\}\) of \(B^3 = \{x\in {\Bbb R}^3 : |x| \le 1\}\) such that \(P_i\) is congruent to \(S_i\) for \(1\le i\le n\) and \(Q_i\) is congruent to \(T_i\) for \(1\le i\le r\).

313

\(\Bbb Z\) (the set of integers under addition) is amenable.  (\(G\) is {\it amenable} if there is a finitely additive measure \(\mu\) on \(\cal P(G)\) such that \(\mu(G) = 1\) and \(\forall A\subseteq G, \forall g\in G\), \(\mu(gA)=\mu(A)\).)

363

There are exactly \(2^{\aleph_0}\) Borel sets in \(\Bbb R\). G. Moore [1982], p 325.

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 \(m\), \(2m = m\).
62

\(C(\infty,< \aleph_{0})\):  Every set of non-empty finite  sets  has  a choice function.

67

\(MC(\infty,\infty)\) \((MC)\), The Axiom of Multiple Choice: For every set \(M\) of non-empty sets there is a function \(f\) such that \((\forall x\in M)(\emptyset\neq f(x)\subseteq x\) and \(f(x)\) is finite).

151

\(UT(WO,\aleph_{0},WO)\) (\(U_{\aleph_{1}}\)): The union of a well ordered set of denumerable sets is well  orderable. (If \(\kappa\) is a well ordered cardinal, see note 27 for \(UT(WO,\kappa,WO)\).)

163

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

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.

324

\(KW(WO,WO)\), The Kinna-Wagner Selection Principle for a well ordered family of well orderable sets: For every well ordered set \(M\) of well orderable sets, there is a function \(f\) such that for all \(A\in M\), if \(|A| > 1\) then \(\emptyset\neq f(A)\subsetneq A\). (See Form 15.)

330

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

344

If \((E_i)_{i\in I}\) is a family of non-empty sets, then there is a family \((U_i)_{i\in I}\) such that \(\forall i\in I\), \(U_i\) is an ultrafilter on \(E_i\).

Historical background: Let \(\Gamma\) be the group of all even permutationson \(\omega\). \(\cal G = \{g:(\forall\alpha\in\omega_1)(\exists\gamma\in\Gamma) (\forall i\in\omega) g(a_{i,\alpha})=a_{\gamma(i),\alpha}\) and for all but finitely many \(\alpha\in\omega_1,(\forall i\in\omega)(g(a_{i,\alpha}) = a_{i,\alpha})\}\). \(S\) is the setof all countable subsets of \(A\). This is the model of proposition 3.4 inBrunner/Howard [1992]. In this model, \(|A|<|A|+|A|\) (3 isfalse). The axiom of choice for a denumerable set of sets (8) is true andit is also true that every infinite set is the union of a disjoint wellorderable family of denumerable sets (152 is true). If \(B_{\alpha}=\{a_{i, \alpha}: i\in\omega\}\), then \(\bigcup\{B_{\alpha}:\alpha\in\omega_1\}\) cannot be well ordered (151 is false), but the unionof a well ordered family of finite sets can be well ordered ([122 A] istrue). \(C(\infty,WO)\) (60) implies 151 and in every FM model\(C(\infty,<\aleph_0)\) (62) implies 60 (Howard [1973]). Thus, 62is false. It follows from Brunner [1982a] that in this modelthere is a set that cannot be well ordered and does not have an infiniteDedekind finite subset, (163 is false). (Form 8 plusForm 163 iff AC.)Since 8 implies 9 (Every Dedekind finite set is finite.) and 70 (There isa non-trivial ultrafilter on \(\omega\).) is true in every FM model, itfollows that 63 (every infinite set has a non-trivial ultrafilter) is alsotrue. Blass [1979] has shown that 191 (There is a set \(X\) suchthat for each set \(a\) there is an ordinal \(\alpha\) and a function \(f\)mapping \(X\times\alpha\) onto \(a\).) is true in every permutation model witha set of atoms. He has also shown that 8 + 191 + 193 (Every Abelian groupis a homomorphic image of a free projective Abelian group.) iff AC. Thus,193 is false. (See Note 60 for definitions.) \(KW(WO,WO)\) (324) and\(MC(WO,WO)\) (330) are false because \(\{B_\alpha:\alpha\in\omega_1\}\) is awell ordered set of well orderable sets that has no Kinna-Wagner selectionfunction and no multiple choice function. In Note 144 we show dependentchoice (form 43) is true and in Note 155 we show that ``every set isalmost well orderable'' (form 144) is false.

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