[EM] 1-Person-1-Vote has been abandoned.
Narins, Josh
josh.narins at lehman.com
Wed Jan 15 13:17:34 PST 2003
Which, although too much to digest in a single read-through, perfectly
segues into a crazy idea I had the other day.
Game Theory is a geometry, someone told me.
The difficult part of voting math is often the cyclical nature of certain
results (A>B B>C C>A) (anyone who reads this list can come to that
conclusion quickly enough)
Ergo...
use a non-euclidian geometry.
um, maybe I just meant...
use a spherical geometry.
Maybe arrow's theorem won't even apply with a limitation like "the voter
space is finite" (like a sphere has a definite size, whereas a plane does
not)
or maybe i'm "mixing metaphors" (mixing mathematics)
-JOSH NARINS (hypothetically proud)
-----Original Message-----
From: Forest Simmons [mailto:fsimmons at pcc.edu]
Sent: Wednesday, January 15, 2003 3:58 PM
To: election-methods-list at eskimo.com
Subject: Re: [EM] 1-Person-1-Vote has been abandoned.
Actually, Cantor proved that there are infinitely many distinct infinities
on the same day he proved that the cardinality of the reals is greater than
the cardinality of the rationals.
Here's the proof in modern notation:
Let X be any set (finite or infinite, it doesn't matter). Let P(X) be the
power set of X, i.e. the collection of all subsets of X.
Then while there is a one-to-one function from X into P(X), there is no
function from X onto P(X).
In other words, the cardinality of P(X) is strictly greater than the
cardinality of X.
Let N be the set of natural numbers and (for any set A) let #A represent the
cardinality of A.
Then #N < #P(N) < #P(P(N)) < #P(P(P(N))), etc.
Details:
An example of a one-to-one function from X into P(X) is the function given
by f(x)={x}, i.e. the image of any member of X is the singleton subset for
which it is the only member.
To show that no function maps X onto P(X), suppose to the contrary that g is
such a function.
Then let Y be the member of P(X) defined by
{ x | x is not a member of g(x)}.
Since Y is a member of P(X), and g maps X onto P(X), there must be some
member x of X such that g(x)=Y.
Note that according to the definition of Y, this x is an element of Y if and
only if it is not an element of Y.
This contradiction shows the non-existence of any such map g.
This is the famous diagonal argument of Cantor slightly disguised.
Note that the points of the middle thirds Cantor set are in one to one
correspondence with the base three "decimal" expansions that have no
occurrence of the digit 1 .
These expansions are, in one to one correspondence with subsets of N.
For example x=.20020222202... corresponds to the subset
h(x)={1,4,6,7,8,9,11,...}. In general
h(x)={ n | the n_th digit of x is a two (in the base three expansion)}.
So the Cantor set, which is a subset of the reals has the same cardinality
as the power set of the natural numbers.
Another of Cantor's ingenious arguments showed that the Naturals have the
same cardinality as the Rationals.
He was unable to answer the question of whether there might be other
cardinalities between those of the Naturals and the Reals.
Godel constructed a model of set theory in which there is no such
cardinality.
Later Cohen constructed a model in which there are infinitely many such
cardinalities.
So just as there are both Euclidean and non-Euclidean geometries, there are
Cantorian and Non-Cantorian set theories.
In other words, the "Continuum Hypothesis" is just as logically independent
of the other basic axioms of set theory as the parallel postulate is
independent from the other axioms of geometry.
Forest
On Wed, 15 Jan 2003, Eric Gorr wrote:
>
> I am assuming that no one has discovered another level of infinity.
>
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