1
P
0
1
INCOMPLETENESS
by
Harvey M. Friedman
December 3, 2005
"Beautiful" is a word used by mathematicians with a semi
rigorous meaning.
We give "arguably beautiful" explicitly Pi01 sentences
independent of ZFC. See Proposition A from section 1, and
variants.
1.
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0
1
INDEPENDENT STATEMENTS USING ANTICHAINS.
We use [1,n] for the discrete interval {1,.
..,n}.
Let A [1,n]
k
. We write A’ = [1,n]
k
\A. This treats [1,n]
k
as the ambient space.
Let R [1,n]
2k
. We define
RA = R[A] = {y [1,n]
k
: (
$
x A)(R(x,y))}.
We say that R is strictly dominating if and only if for all
x,y [1,n]
k
, if R(x,y) then max(x) < max(y).
We start with a basic finite fixed point theorem.
THEOREM 1.1. For all k,n
≥
1 and strictly dominating R
[1,n]
2k
, there exists A [1,n]
k
such that R[A’] = A.
Furthermore, A [1,n]
k
is unique.
We can obviously take complements, obtaining what we call
the ‘complementation theorem’ for RA.
THEOREM 1.2. For all k,n
≥
1 and strictly dominating R
[1,n]
2k
, there exists A [1,n]
k
such that RA = A’.
Furthermore, A [1,n]
k
is unique.
For A [1,n]
k
and t
≥
1, we write A\t = {x A: t is not a
coordinate of x} = "A with t omitted".
Here is a modification of Theorem 1.1 which we call the
‘complementation theorem’ for R[A\2
(8k)!
-1].