# [FOM] 239:Pi01 Update

Harvey Friedman friedman at math.ohio-state.edu
Sat Dec 11 13:12:45 EST 2004

```This is an update on postings 237 and 238.

1. We no longer need to use variable length cross sections.

2. We have to expand the class of restricted affine functions used in
posting 237. We should have used affine transformations restricted to
semilinear sets. We are not sure that we can get away with the smaller class
used in posting 237.

3. In fact, we now use restricted linear functions. I.e., restricted to
semilinear sets.

I *think* that this round has settled down.

These developments in no way, shape, or form obsolete BRT.

##########################################

Let N be the set of all nonnegative integers. Let T:N^k into N, and V
containedin N^k. We define the upper image of T on V by

T<[V] = {T(x): x in V and T(x) > max(x)}.

We use U. for disjoint union. Thus A U. B is A U B if A,B are disjoint;
undefined otherwise.

THEOREM 1. For all T:N^k into N, some A U. T<[A^k] is N. In fact, A is
unique.

Theorem 1 has the following finite form.

THEOREM 2. For all T:[p]^k into N, some A U. T<[A^k] contains rng(T).

We will use two classes of functions.

We write PL([p]^k,E) for the set of all piecewise linear transformations
T:[p]^k into N over E. These are the T:[p]^k into N defined by finitely many
cases, where each case is given by a finite set of linear inequalities, and
T is given by an affine expression with coefficients in each case, and where
all coefficients used in the inequalities and affine expressions lie in E.

We write RL([p]^k,E) for the set of all restricted linear transformations
T:[p]^k into N over E. These are the partial T:[p]^k into N defined by a
linear transformation restricted to a semilinear set, where all coefficients
used in the semilinear set and the linear expression lie in E.  Here a
semilinear set is given by a Boolean combination of linear inequalities).

We take min(emptyset) = 0. For y in N^k, we define y! = (y_1!,...,y_k!).

PROPOSITION 3. For all T in PL([p]^2k,[k]), some A U. T<[A^k] contains all
min(T[A^k x {y!}]) and omits (8k)!!-1.

PROPOSITION 4. For all T in RL([p]^2k,[k]), some A U. T<[A^k] contains all
min(T[A^k x {y!}]) and omits (8k)!!-1.

We can instead use symmetric difference.

PROPOSITION 5. For all T in PL([p]^2k,[k]), some A delta T<[A^k] contains
all min(T[A^k x {y!}]) and omits (8k)!!-1.

PROPOSITION 6. For all T in RL([p]^2k,[k]), some A delta T<[A^k] contains
all min(T[A^k x {y!}]) and omits (8k)!!-1.

Propositions 3-6 are easily seen to be Pi01, since we can obviously bound
the A and the y!.

As things stabilize, we will sharpen the (8k)!!.

THEOREM 7. Theorem 1 is provable in RCA0 and Theorem 2 is provable in EFA.
Propositions 3-6 are each provably equivalent, over ACA, to the consistency
of MAH = ZFC + {there exists an n-Mahlo cardinal}_n. If we remove
"omits (8k)!!-1", then they become immediate consequences of Theorem 2, and
hence provable in EFA.

If we set p to be certain simple functions of k, rather than arbitrary, then
we can control the strength of Proposition 3 somewhat. We should be able
to get PA and n-th order arithmetic, for various n, as well as significant
fragments of ZFC, ZFC itself, and levels of the Mahlo hierarchy.

We now present much stronger Pi01 statements.

Let R1,...,Rt,S1,...,St be multivariate relations on N, where the arity of
each Ri,Si are the same. Let E contianedin N. We say that

f nontrivially embeds (N,R1,...,Rt) into (N,S1,...,St) over D

if and only if

i) f is a partial function from V into V that is not an identity function;
ii) for all x1,...,xn in dom(f), Ri(x1,...,xn) iff Si(f(x1),...,f(xn)),
where the arity of Ri is n;
iii) D containedin dom(f).

For A containedin N^k, let d(A) = {n: (n,...,n) in A}.

PROPOSITION 8. For all T in PL([p]^6k,[k]) there exists A containedin [p]^3
such that each A_i! embeds ([i!],T,d(A),T<[A^2k]) into
([i!]\{(8k)!!},T,d(A),d(A)') over all min(T[A^k x {y!}]) < i! < p.

PROPOSITION 9. For all T in RL([p]^6k,[k]) there exists A containedin [p]^3
such that each A_i! embeds ([i!],T,d(A),T<[A^2k]) into
([i!]\{(8k)!!},T,d(A),d(A)') over all min(T[A^k x {y!}]) < i! < p.

Propositions 8,9 are obviously explicitly Pi01.

THEOREM 10. Propositions 8,9 are provably equivalent, over EFA, to the
consistency of ZFC + {there exists an n-Mahlo cardinal lambda such that
there are lambda many kappa < lambda with a nontrivial elementary embedding
from V(kappa) into V(kappa)}_n.

*************************************

This is the 239th in a series of self contained numbered postings to
FOM covering a wide range of topics in f.o.m. The list of previous
numbered postings #1-149 can be found at
http://www.cs.nyu.edu/pipermail/fom/2003-May/006563.html  in the FOM
archives, 5/8/03 8:46AM. Previous ones counting from #150 are:

150:Finite obstruction/statistics  8:55AM  6/1/02
151:Finite forms by bounding  4:35AM  6/5/02
152:sin  10:35PM  6/8/02
153:Large cardinals as general algebra  1:21PM  6/17/02
154:Orderings on theories  5:28AM  6/25/02
155:A way out  8/13/02  6:56PM
156:Societies  8/13/02  6:56PM
157:Finite Societies  8/13/02  6:56PM
158:Sentential Reflection  3/31/03  12:17AM
159.Elemental Sentential Reflection  3/31/03  12:17AM
160.Similar Subclasses  3/31/03  12:17AM
161:Restrictions and Extensions  3/31/03  12:18AM
162:Two Quantifier Blocks  3/31/03  12:28PM
163:Ouch!  4/20/03  3:08AM
164:Foundations with (almost) no axioms 4/22/03  5:31PM
165:Incompleteness Reformulated  4/29/03  1:42PM
166:Clean Godel Incompleteness  5/6/03  11:06AM
167:Incompleteness Reformulated/More  5/6/03  11:57AM
168:Incompleteness Reformulated/Again 5/8/03  12:30PM
169:New PA Independence  5:11PM  8:35PM
170:New Borel Independence  5/18/03  11:53PM
171:Coordinate Free Borel Statements  5/22/03  2:27PM
172:Ordered Fields/Countable DST/PD/Large Cardinals  5/34/03  1:55AM
173:Borel/DST/PD  5/25/03  2:11AM
174:Directly Honest Second Incompleteness  6/3/03  1:39PM
175:Maximal Principle/Hilbert's Program  6/8/03  11:59PM
176:Count Arithmetic  6/10/03  8:54AM
177:Strict Reverse Mathematics 1  6/10/03  8:27PM
178:Diophantine Shift Sequences  6/14/03  6:34PM
179:Polynomial Shift Sequences/Correction  6/15/03  2:24PM
180:Provable Functions of PA  6/16/03  12:42AM
181:Strict Reverse Mathematics 2:06/19/03  2:06AM
182:Ideas in Proof Checking 1  6/21/03 10:50PM
183:Ideas in Proof Checking 2  6/22/03  5:48PM
184:Ideas in Proof Checking 3  6/23/03  5:58PM
185:Ideas in Proof Checking 4  6/25/03  3:25AM
186:Grand Unification 1  7/2/03  10:39AM
187:Grand Unification 2 - saving human lives 7/2/03 10:39AM
188:Applications of Hilbert's 10-th 7/6/03  4:43AM
189:Some Model theoretic Pi-0-1 statements  9/25/03  11:04AM
190:Diagrammatic BRT 10/6/03  8:36PM
191:Boolean Roots 10/7/03  11:03 AM
192:Order Invariant Statement 10/27/03 10:05AM
193:Piecewise Linear Statement  11/2/03  4:42PM
194:PL Statement/clarification  11/2/03  8:10PM
195:The axiom of choice  11/3/03  1:11PM
196:Quantifier complexity in set theory  11/6/03  3:18AM
197:PL and primes 11/12/03  7:46AM
198:Strong Thematic Propositions 12/18/03 10:54AM
200:Advances in Sentential Reflection 12/22/03 11:17PM
201:Algebraic Treatment of First Order Notions 1/11/04 11:26PM
202:Proof(?) of Church's Thesis 1/12/04 2:41PM
203:Proof(?) of Church's Thesis - Restatement 1/13/04 12:23AM
204:Finite Extrapolation 1/18/04 8:18AM
205:First Order Extremal Clauses 1/18/04 2:25PM
206:On foundations of special relativistic kinematics 1 1/21/04 5:50PM
207:On foundations of special relativistic kinematics 2  1/26/04  12:18AM
208:On foundations of special relativistic kinematics 3  1/26/04  12:19AAM
209:Faithful Representation in Set Theory with Atoms 1/31/04 7:18AM
210:Coding in Reverse Mathematics 1  2/2/04  12:47AM
211:Coding in Reverse Mathematics 2  2/4/04  10:52AM
212:On foundations of special relativistic kinematics 4  2/7/04  6:28PM
213:On foundations of special relativistic kinematics 5  2/8/04  9:33PM
214:On foundations of special relativistic kinematics 6  2/14/04 9:43AM
215:Special Relativity Corrections  2/24/04 8:13PM
216:New Pi01 statements  6/6/04  6:33PM
217:New new Pi01 statements  6/13/04  9:59PM
218:Unexpected Pi01 statements  6/13/04  9:40PM
219:Typos in Unexpected Pi01 statements  6/15/04  1:38AM
220:Brand New Corrected Pi01 Statements  9/18/04  4:32AM
221:Pi01 Statements/getting it right  10/7/04  5:56PM
222:Statements/getting it right again  10/9/04  1:32AM
223:Better Pi01 Independence  11/2/04  11:15AM
224:Prettier Pi01 Independence  11/7/04  8:11PM
225:Better Pi01 Independence  11/9/04  10:47AM
226:Nicer Pi01 Independence  11/10/04  10:43AM
227:Progress in Pi01 Independence  11/11/04  11:22PM
228:Further Progress in Pi01 Independence  11/12/04  2:49AM
229:More Progress in Pi01 Independence  11/13/04  10:41PM
230:Piecewise Linear Pi01 Independence  11/14/04  9:38PM
231:More Piecewise Linear Pi01 Independence  11/15/04  11:18PM
232:More Piecewise Linear Pi01 Independence/correction  11/16/04  8:57AM
233:Neatening Piecewise Linear Pi01 Independence  11/17/04  12:22AM
234:Affine Pi01 Independence  11/20/04  9:54PM
235:Neatening Affine Pi01 Independence  11/28/04  6:08PM
236:Pi01 Independence/Huge Cardinals  12/2/04  3:49PM
237:More Neatening Pi01 Affine Independence  12/6/04  12:56AM
238:Pi01 Independence/Large Large Cardinals/Correction  12/7/04  10:31PM

Harvey Friedman

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