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Ross A. Finlayson  
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 More options Nov 24 2006, 8:54 pm
Newsgroups: sci.math
From: "Ross A. Finlayson" <r...@tiki-lounge.com>
Date: 24 Nov 2006 17:54:46 -0800
Local: Fri, Nov 24 2006 8:54 pm
Subject: Re: Infinity Again

Albrecht wrote:
> On 22 Nov., 04:37, "Ross A. Finlayson" <r...@tiki-lounge.com> wrote:
> > > Those are old hat, the question in which I have particular interest at
> > > this time is if via a method to select at uniform random an element or
> > > infinitely many elements of the real numbers whether via a pretty
> > > simple construction that can be construed as a method to select a
> > > natural integer at uniform random, as I have so described.About this notion of a bijection between the unit interval of reals and
> > N^N, in standard ways, and about some informal consideration of the
> > N-choice sequences or in shorthand N-sequences being uniformly dense
> > within the elements of N^N, I should enumerate an obvious progression
> > of reasoning to that effect.

> > Basically the sketch is this:  the reals in the unit interval biject to
> > N^N, the cartesian product of infinitely many copies of the natural
> > integers.  There exists a uniform probability distribution over the
> > unit interval of reals, and thus the elements of N^N, in that each
> > element of N^N so correlated, informally, has an equal probability of
> > being selected as a sample as does any element in R[0,1].

> > Now, among all those elements of N^N, very very few of them are
> > N-sequences, sequences with each element of the natural integers being
> > an element of the sequence exactly once, where those are ranges of
> > choice functions, well-orderings of the natural integers and have a
> > least, in this case first, element of the sequence.  None of those
> > sequences are identical.  So, sample from N^N at uniform random and
> > discard the sample if it is not an N-sequence, and sample until there
> > is an N-sequence, selected at uniform random from among the
> > N-sequences.

> > Then, each N-sequence in N^N has the same probability of being
> > selected.  As samples of the natural integers, let the N-sequences that
> > begin with n be N(n)-sequences, N sequences that begin with x, y, z
> > being N(x, y, z)-sequences, for and etcetera, for a finite number of
> > variables.  There is an N(n)-sequence for each n, finite natural
> > integer in N.

> > The N(n)-sequences can be considered identical, the elements of the
> > sequence after the first are inconsequential.

> > Then that seems to beg the question of there being a natural uniform
> > probability distribution over the natural integers for there to be one.

> > While that may be so, each of the N(n)-sequences has the same
> > probability of being selected as any other, as each is an element of
> > N^N.  So, it may be disregarded which one it is.

> > I'm not sure about bijecting R[0,1] to N^N, but it seems that if it
> > took R^N to biject to N^N then R would biject to N.  Otherwise there
> > would be cardinals between those of N and P(N).

> > Taking infinitely many samples of R to sample N^N is the same as
> > sampling infinitely many samples of {0,1} to sample R, and that returns
> > infinitely many samples.  That process returning a rational would
> > return infinitely many copies of a variety of rationals, and returning
> > an algebraic irrational would seem to return only algebraics.
> > Returning zero means all zeros.

> > So, yeah, that's why.

> > Ross

> I'm not sure whether I'm understanding this argument completely, so I'm
> interested in comments about it.
> My understanding: Since there are no functions which covers all reals
> we have to use probabilistic methods to find something out. Using this
> ansatz, we find no difference between the frequency of reals and
> naturals.
> Is this, roughly said, correct?
> Comments?

> Best regards
> Albrecht S. Storz

Hello,

Well, it is what it is: from a bijection from as many copies of R[0,1]
as necessary to N^N, sample until an N-sequence results, and consider
that's first element a natural integer at uniform random, because each
of the N(n)-sequences has the same probability of being selected.
(Where each N-sequence and thus each N(n)-sequence has the same
probability of being selected, due to the existence of a uniform
distribution over [0, 1], that each n has the same probability of being
selected is partially as described above, where arguments of symmetry
and isometry are readily presentable.)

I don't know what you mean when you say "no function covers all reals."
 Do you mean functions with domain the natural integers?  Then I think
EF is a bijection between N and R[0,1].  Conveniently its integral over
the domain is one and each value of the range is greater than or equal
to zero.  That's quite obvious.

In correspondence with counterexamples to standard real analysis, with
such notions as an iota value or least positive real, you might see why
that makes sense.

Ross


 
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