Fraenkel \(\cal N2(n,M)\): Mostowski's variation of \(\cal N2(n)\) | Back to this models page

Description: \(A\), \(B\), and \(S\)are the same as in \(\cal N2(n)\)

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.

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.

91

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

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}.

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
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(\(n\)).  

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.

192

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

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: In this model, \(\cal G\) is the group ofall permutations of \(A\) such that for each \(\phi\in\cal G\),\(\phi(b_i)=b_i\) (as in \(\cal N2(n)\)), but in addition \(\phi\) is differentfrom the identity on \(b_i\) for at most a finite number of \(i\in\omega\).Let \(K\) be a non-empty set of positive integers. The condition \(M(K,n)\)holds if for every decomposition of \(n\) into a sum of primes,\(n=p_1+p_2+\cdots +p_m\), there is a sequence of \(m\) non-negative integers,\(q_1, q_2,\cdots, q_m\), such that \(p_1q_1 + p_2q_2 +\cdots + p_mq_m\in K\).Mostowski proves that \(C(\infty,K)\) (46) is true in this model if \(M(K,n)\)is false. We shall denote \(C(\infty, K)\) by 46(\(\neg M\)) when condition\(M(K,n)\) is false. Also, it is clear that \(C(WO,n)\) (47(\(n\))) and\(C(\infty,K)\) (46(\(n\in K\))) are false in this model.

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