Fraenkel \(\cal N7\): L\"auchli's Model I | Back to this models page

Description: \(A\) is countably infinite

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
16

\(C(\aleph_{0},\le 2^{\aleph_{0}})\):  Every denumerable collection of non-empty sets  each with power \(\le  2^{\aleph_{0}}\) has a choice function.

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 \(|\bigcup A| = \aleph _{\alpha }\).

24

\(C(\aleph_0,2^{(2^{\aleph_0})})\): Every denumerable collection of non-empty sets each with power \(2^{(2^{\aleph_{0}})}\) has a choice function.

37

Lebesgue measure is countably additive.

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.

123

\(SPI^*\): Uniform weak ultrafilter principle: For each family \(F\) of infinite sets \(\exists f\) such that \(\forall x\in F\), \(f(x)\) is a non-principal ultrafilter on \(x\).

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 \(a\).

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 \(\forall A\subseteq G, \forall g\in G\), \(\mu(gA)=\mu(A)\).)

361

In \(\Bbb R\), the union of a denumerable number of analytic sets is analytic. G. Moore [1982], pp 181 and 325.

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
30

Ordering Principle: Every set can be linearly ordered.

40

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

99

Rado's Selection Lemma: Let \(\{K(\lambda): \lambda \in\Lambda\}\) be a family  of finite subsets (of \(X\)) and suppose for each finite \(S\subseteq\Lambda\) there is a function \(\gamma(S): S \rightarrow X\) such that \((\forall\lambda\in S)(\gamma(S)(\lambda)\in K(\lambda))\).  Then there is an \(f: \Lambda\rightarrow X\) such that for every finite \(S\subseteq\Lambda\) there is a finite \(T\) such that \(S\subseteq T\subseteq\Lambda\) and such that \(f\) and \(\gamma (T)\) agree on S.

133  

Every set is either well orderable or has an infinite amorphous subset.

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.)

192

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

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: The group \(\calG\) is a permutation group on \(A\) with the following properties:\item{1.} If \(E_1\) and \(E_2\) are finite subsets of \(A\) and if \(\phi\in\cal G\) is the identity on \(E_1\cap E_2\), then there exist \(\pi_i\) and\(\rho_i\) in \(\cal G\), \(i = 1,2,\cdots n\), such that \(\phi=\pi_1\cdot\rho_1\cdot\pi_2\cdot\rho_2\cdots\pi_n\cdot\rho_n\) where \(\pi_i\) is theidentity on \(E_1\) and \(\rho_i\) is the identity on \(E_2\).\item{2.} If \(E\) is a finite subset of \(A\) and \(\phi\in\cal G\) issuch that \(\phi(E)=E\), then \(\phi\) is the identity on \(E\).\item{3.} For each finite \(E\subset A\), there are distinct elements\(a,b,c\in A\) and \(\phi,\rho\in\cal G\) which are the identity on \(E\) suchthat \(\phi: a\mapsto b\mapsto c\) and \(\rho: c\mapsto a\mapsto b\).\(S\) is the set of all finite subsets of \(A\). L\"auchli proves that in thismodel, AC for a set of finite sets (62) and AC for a set of well orderablesets (60) are true, but the Ordering Principle (30) is false. Since 60implies \(UT(WO,WO,WO)\) (231) and in every FM model 231 implies\((\forall\alpha)UT(\aleph_{\alpha}, \aleph_{\alpha},\aleph_{\alpha})\),form 23 is true. Also, 60 implies that there is no amorphous set (64 istrue), and 64 implies 133 (Every set is either well orderable or has aninfinite amorphous subset.) is false. Pincus proves that there is afunction which associates each infinite set with a nonprincipal ideal inits power set (123 is true). Moreover, Rado's Lemma (99) is false in thismodel because BPI (14) is false (14 implies 30) and 99 + 62 implies 14(Note 33). Since 60 is true, AC for a well ordered set of sets (40) isfalse. (See Howard/Rubin [1995b].)Form 40 is false andForm 122(\(C(WO,<\infty)\)) is true because 60 implies 122. Therefore,Form 328(\(MC(WO,\infty)\)) is false because \(122 + 328\to 40\). SinceForm 165(\(C(WO,WO)\)) is true, (60 implies 165) it follows from Note 2(8 and 9)that 16 and 24 are also true.

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