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  [FAQ, 06/11/05] Mathematical logic on the web         


Author: Boris 'pi' Piwinger
Date: Jan 31, 2008 17:03

Mathematical Logic around the world:
http://world.logic.at/
--
Posted: Fri Feb 1 01:03:01 2008
no comments
  Re: Heap-Set Theory H-S         


Author:
Date: Jan 31, 2008 16:41

On Wed, 30 Jan 2008 14:19:23 -0800 (PST), lwalke3@lausd.net wrote:
>
> What I thought is particularly striking is
> Frege's proof ...
>
Yes, he's still with us! :-)
>
> ... that for every heap x, x = [x].
>
Proof? Did I present a proof for that? I must have missed it. :-)

Anyway, I can present an _argument_ for it: a heap consisting of a
single object (say a grain of sand) _is_ just that single object
(grain of sand). Hence: a = [a] (where a is "atomic"). On the other
hand, a heap [A] consisting of a heap A is just that heap A. Again:
[A] = A (for a heap A). Hence for every heap x: x = [x].
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10 Comments
  Re: FOL vs 2OL         


Author: LauLuna
Date: Jan 31, 2008 16:04

On Jan 31, 5:07 am, Bill Taylor math.canterbury.ac.nz>
wrote:
> From another thread, someone said:
>
>> Actually, to bring up an old point again, although it is perfectly
>> standard and a handy way of talking, from a certain point of view
>> it might be thought strange to call first order PA "arithmetical" and
>> not use the same word for a second order arithmetic statement.
>
> It might seem strange at first, but it seems to be
> a useful distinction, at least as a facon de parler.
>
> It highlights the fact that whereas FOL PA is about numbers, 2OL
> is essentially about sets; taking Quine's critique as substantial.
>
>> some true properties of numbers require second order quantifiers
>> to even state them, let alone prove them.
>
> Essentiallythough, these are statements not about
> numbers per se, but essentially about SETS of numbers. ...
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no comments
  Are Locke's "degrees of assent" one method for deciding between two theories which both have some evidence?         


Author: Immortalist
Date: Jan 31, 2008 15:50

In ECHU IV.15.2, John Locke introduces the notion of 'degrees of
assent'. On the basis of this notion he formulates his claim in IV.
16.1 that the degrees of assent should be regulated by the degrees of
probability. This is a fairly common view in modern philosophy; you
can call to mind, for instance, Hume's famous saying, "The wise man
proportions his belief to the evidence," which Hume means quite
literally: the degree of belief should match the degree of evidence.

http://branemrys.blogspot.com/2004/12/are-there-degrees-of-assent.html

So, apart from the few important things that we can know for certain,
e.g. the existence of ourselves and God, the nature of mathematics and
morality broadly construed, for the most part we must lead our lives
without knowledge. What then is probability? Locke writes:

As Demonstration is the shewing of the agreement or disagreement of
two Ideas, by the intervention of one or more Proofs, which have a
constant, immutable, and visible connexion one with another: so
Probability...
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no comments
  Re: flat sun theory - REALLY SERIOUS         


Author: Phil Cartwright
Date: Jan 31, 2008 14:18

hagman wrote:
> The dust cloud the planets (and the sun) have fromed from was (or
> somehow
> became) more or less a flat disk.

Any big sparse sphere of dust with nonzero angular momentum, when
allowed to contract (e.g. under gravity), will become a nearly flat disk
as it much more easily shrinks along the spin axis (no centrifugal
effects) than in the plane of rotation (due to centrifugal effects).

As for why it had nonzero angular momentum, the probability of a
specific angular momentum vector, including the zero vector, is zero so
you "almost certainly" get something else given a random clump of space
molecules. C.f. "why does everything spin?" posted a week or two ago.

--
There's only four things you can be certain of: taxes, change, spam, and
death.
no comments
  Re: What logical fallacy is this?         


Author: Ouroboros_Rex
Date: Jan 31, 2008 09:36

yahoo.com> wrote in message
news:819a2bb1-8219-4b84-9175-358b72f4bd1b@e23g2000prf.googlegroups.com...
>
> Suppose I am trying to explain some complex set of evidence,
> of many things that collectively point to a conclusion,
> but before I can even get the first piece of evidence
> expressed, the person quickly dismisses it
> using very specious logic, pretends that I've already
> expressed the whole of my argument, pretends
> that they've disproven the whole argument, and
> acts like the conclusion was totally false and a crazy
> conclusion to reach.
>
> Which logical fallacy are they committing?

Straw Man. They mischaracterized your argument in order to gain their
foothold.
no comments
  Re: A consideration concerning the diagonal argument of G. Cantor         


Author: MoeBlee
Date: Jan 31, 2008 09:34

On Jan 30, 10:51 pm, WM wrote:
> |{ x | x in S(n) & x > |S(n)| }| / |S(n)| = 1/2       [#]

No, you've not defined an operation of division on cardinals.
Definition of an operation requires proving uniqueness and existence
clauses and then proper definitional form. You've not even hinted at
anything like that. As usual, your idea of mathematical argument is to
force whatever conclusion you desire by resort to undefined
terminology.

MoeBlee
1 Comment
  Re: A consideration concerning the diagonal argument of G. Cantor         


Author: Daryl McCullough
Date: Jan 31, 2008 07:51

WM says...
>
>On 30 Jan., 23:07, "Jesse F. Hughes" phiwumbda.org> wrote:
>> It is a basic fact that the infinite set N has only finite elements.
>
>The elements can be understood as initial sequences like
>
>1
>1,2
>1,2,3
>...
>
>With respect to the assumption that all are there and have cardinality
>aleph_0, you say that the union of such finite sequences is an
>infinite sequence.

Yes, and that is exactly what happens. If you have an infinite
collection of finite sets, then the union is infinite.
>In set theory this is impossible.

On the contrary, that's exactly what happens in set theory.
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147 Comments
  The problem of action         


Author: Akash
Date: Jan 31, 2008 07:23

Action implies a close connection between objects. All persons are
entitled to act; but the manner of action of each is different. The
actor maybe described as a man; but the term "man" refers to the whole
human species, and so a woman is an actor too. But if the term "man"
expressly refers to the male, it should be taken to be so.

There are some who believe that a woman cannot own property; but she
can do so; only she is second to man; but what belongs specially to
her is the power to bless and to remain chaste.

A further discussion on the subject maybe read at:

http://www.narachphilosophy.com/the_problem_of_action.htm

(You may click on the link above or type the complete URL address into
your browser)
2 Comments
  Toposes and Proper Classes         


Author: Mattias Wikstrom
Date: Jan 31, 2008 05:24

Let us call an object M in a category C a "proper class object" if for
every object N in C there is a monic arrow f:N->M.

A topos cannot have a proper class object (since objects in a topos
are required to have power objects), but given a topos T, we can
extend it into a category which does include a proper class object. To
be precise, we can find a category which has a subcategory equivalent
to T and in which any object not in this subcategory is a proper class
object.

For example, we can extend the topos FinSets into a category which we
may call FinSets* which in addition to finite sets includes a natural
numbers object, but which does not include anything besides this.
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3 Comments
 
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