Fraenkel \(\cal N32\): Hickman's Model III | Back to this models page

Description: This is a variation of \(\cal N1\)

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.

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(\(n\)).  

192

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

237

The order of any group is divisible by the order of any of its subgroups, (i.e., if \(H\) is a subgroup of \(G\) then there is a set \(A\) such that \(|H\times A| = |G|\).)

238

Every elementary Abelian group (that is, for some prime \(p\) every non identity element has order \(p\)) is the direct sum of cyclic subgroups.

240

If a group \(G\) satisfies "every ascending chain of subgroups is finite", then every subgroup of \(G\) is finitely generated.

Historical background: Let \(A\)be denumerable. Construct an elementary Abelean \(p\)-group \(G\) on \(A\) where\(p\) is a prime. (Every non-identity element has order \(p\).) Let \(\cal G\)be the group of automorphisms of \(G\), and let \(S\) be the set of finitesubsets of \(A\). Hickman proves that if \(H\) is any non-trivial subgroup of\(G\), then the order of \(H\) does not divide the order of \(G\) (237 isfalse). Thus, it follows that \(G\) is not the direct sum of cyclic groups(238 is false). Hickman also shows that in \(G\) every ascending chain ofsubgroups is finite, but \(G\) is not finitely generated (240 is false).

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