Fraenkel \(\cal N2(n)\): A generalization of \(\cal N2\) | Back to this models page

Description: This is a generalization of\(\cal N2\) in which there is a denumerable set of \(n\) element sets for\(n\in\omega - \{0,1\}\)

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
6

\(UT(\aleph_0,\aleph_0,\aleph_0,\Bbb R)\): The union of a denumerable  family  of denumerable subsets of \({\Bbb R}\) is denumerable.

37

Lebesgue measure is countably additive.

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).

130

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

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}.

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.

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
46-K

If \(K\) is a finite subset of \(\omega-\{0,1\}\), \(C(\infty,K)\): For every \(n\in K\), every set of \(n\)-element sets has a choice function.

47-n

If \(n\in\omega-\{0,1\}\), \(C(WO,n)\): Every well ordered collection of \(n\)-element sets has a choice function.

154

Tychonoff's Compactness Theorem for Countably Many \(T_2\) Spaces: The product of countably many \(T_2\) compact spaces is compact.

164

Every non-well-orderable set has an infinite subset with a Dedekind finite power set.

288-n

If \(n\in\omega-\{0,1\}\), \(C(\aleph_0,n)\): Every denumerable set of \(n\)-element sets has 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 \(E_i\).

373-n

(For \(n\in\omega\), \(n\ge 2\).) \(PC(\aleph_0,n,\infty)\): Every denumerable set of \(n\)-element sets has an infinite subset with a choice function.

Historical background: \(A=\bigcup B\), where \(B\) is a set of pairwisedisjoint \(n\) element sets \(b_i\) with \(i\in\omega\); \(\cal G\) is the groupof all permutations that leave \(B\) point-wise fixed (\(\phi(b_i)=b_i\) foreach \(i\in\omega\)); and \(S\) is the set of all finite subsets of \(A\). Inthis model, the Axiom of Multiple Choice (67) is true, but \(C(WO,n)\)(47(\(n\))), \(C(\aleph_0,n)\) (288(\(n\))) and \(PC(\aleph_0,n,\infty)\)(373(\(n\))) are false. Let \(K\) be a non-empty set of positive integers,then for \(n\in K\), \(C(\infty,K)\) is false. For \(n\in K\), we shall denote\(C(\infty,K)\) by 46(\(n\in K\)).

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