Fraenkel \(\cal N24\): Hickman's Model I | Back to this models page

Description: This model is a variation of \(\cal N2\)

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
10

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

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.

121

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

130

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

133  

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

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

340

Every Lindelöf metric space is separable.

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.

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
64

\(E(I,Ia)\) There are no amorphous sets. (Equivalently, every infinite set is the union of two disjoint infinite sets.)

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).

124

Every operator on a Hilbert space with an amorphous base is the direct sum of a finite matrix and  a  scalar operator.  (A set is amorphous if it is not the union of two disjoint infinite sets.)

127

An amorphous power of a compact \(T_2\) space, which as a set is well orderable, is well orderable.

131

\(MC_\omega(\aleph_0,\infty)\): For every denumerable family \(X\) of pairwise disjoint non-empty sets, there is a function \(f\) such that for each \(x\in X\), f(x) is a non-empty countable subset of \(x\).

132

\(PC(\infty, <\aleph_0,\infty)\):  Every infinite family of finite  sets has an infinite subfamily with a choice function.

166

\(PC(\infty,2,\infty)\): Every infinite family of pairs has an infinite subfamily with a choice function.

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\(A=\{a_i : i\in\omega\}\cup \{b_i : i\in\omega\}\), a union of pairwisedisjoint denumerable sets; \(\cal G\) is the group of all permutations on\(A\) such that for each \(\sigma\in\cal G\), and for each \(i\in\omega\),\(\sigma(\{a_i, b_i\})= \{a_j, b_j\}\), for some \(j\in\omega\); and \(S\) isthe set of all finite subsets of \(A\). Then both \(A\) and \(P=\{\{a_i, b_i\}:i\in\omega\}\) are amorphous sets in \(\cal N24\) (64 is false), so itfollows from Brunner [1984a], that in this model there is aHilbert Space \(H\) and an operator on \(H\) which is not the direct sum of afinite matrix and a scalar operator (124 is false). Also, everydenumerable family of finite sets has a choice function (10 is true) andevery linearly ordered family of finite sets has a choice function (121 istrue), but it is not the case that every infinite family of pairs has aninfinite subfamily with a choice function (166 is false). There is anamorphous power of a compact \(T_2\) space which is well orderable, but notcompact (127 is false). In Brunner [1982a], it is shown that ifa set cannot be well ordered, then it has an amorphous subset (133 istrue). It follows from Brunner [1982a] that MC (67) is falsebecause 133 implies 164 (Every non well orderable set has an infinitesubset with a Dedekind finite power set.) and 67 + 164 iff AC. It is shownin Note 123 that 133 implies 231 (\(UT(WO,WO,WO)\)). In every FM model 231implies 23 ((\(\forall\alpha)UT(\aleph_\alpha,\aleph_\alpha,\aleph_\alpha)\)). It follows that 23 is also true. Sinceform 165 (\(C(WO,WO)\)) is true, (133 implies 165) it follows from Note 2(8and 9) that 16 and 24 are also true. It was shown in De la Cruz, Hall,Howard, Keremedis, Rubin [2002a] thatForm 340: Every Lidel\"ofmetric space is separable., is true in this model

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