Re: defn of Named Graph

On Wed, Sep 18, 2013 at 1:33 PM, Jeremy J Carroll <jjc@syapse.com> wrote:

>
>  Something of an aside …
>
> On Sep 18, 2013, at 1:29 AM, Gregg Reynolds <dev@mobileink.com> wrote:
>
> The suggestion that a pair of mathematical entities with exactly the same
> extension are not equal doesn't help - it reads like an attempt to redefine
> mathematics.
>
>
>
> Gregg
>
> I think you misunderstand mathematics ...
>

It's called the Extensionality Axiom.  If x and y have the same elements,
then x is equal to y.  According to Ciesielski, it's one of the two most
basic axioms of set theory.  You may object that set theory does not
exhaust mathematics, but I remind you that we're talking about a technical
specification whose audience consists of working programmers who are
virtually guaranteed to take this axiom for granted.  So if you're going to
claim it does not hold, you have some explaining to do.



> I attach two pictures.
>
> The first is my copy, of Jones' copy of a diagram in a book in the vatican
> library which is a tenth century, maybe fifth generation, copy of a diagram
> drawn by Pappus of Alexandria in the 4th century, which may in turn have
> been a (n-th generational) copy of a diagram drawn by Euclid a few hundred
> years earlier.
> The copy in the vatican library, has, according to Jones, got a mistake in
> it: which he corrected, assuming it to be a copyist's error and not an
> error of Pappus or Euclid.
>
> All these copies will have minor variations .. such as angles and
> distances and sizes being slightly different
>
> In some sense there is one diagram, even the one with a mistake in it,
> which refer to the same mathematical concept. In another sense there are
> multiple diagrams - the one in this e-mail is even in some sense different
> from the one at
> http://oriented.sourceforge.net/images/jones139.jpg which is bitwise
> identical. The intent of the two pictures is quite different - within this
> e-mail I am discussing the meaning of pictures, on that website I am
> interested mainly to compare and contrast with my own picture, the second
> picture here, which, I boldly assert is a picture of the same mathematical
> concept as Pappus' original picture. (My picture and Pappus' original form
> the same arrangement of pseudolines in the projective plane -  concepts
> which had not been invented when Pappus drew his picture)
>

And you would be wrong.  That's a matter of (bad) historical judgment, not
mathematics.  If you see your contemporary mathematical concept in a tenth
century diagram, its because you put it there.  It's a variation on the
Fallacy of Anachronism. You might find Quentin Skinner's "Meaning and
understanding in the history of ideas" enlightening.  You can find a copy
on the web.  If not email me privately and I'll send you a copy.  Another
fascinating account of how this happens is "Lengths, widths, surfaces: a
portrait of old Babylonian algebra and its kin" by Jens Høyrup.  He shows
how the scholars who first reconstructed Babylonian mathematics radically
misread the texts in spite of their brilliance, because they treated their
own historically situated concepts of mathematics for timeless universals
and therefore read them into texts written by people who had no such ideas.

...

>
> The point of all this is that even in mathematics we need to be able to
> talk about the very human tasks relating to copying and changing and making
> my own copy … where notions such as identity move from being obvious to
> being really very subtle.
>

No, the point is that mathematicians make bad historians.


> Sandro is trying to understand the notion of identity that Pat and I see
> as obvious when it comes to graph naming, and by way of technical questions
> trying to probe the subtleties
>

Which I assure you I completely understand.  I made a good faith effort to
contribute to the conversation, to which you responded with an ad homimen
attack.  Nice. I wonder if you even bothered to read my post.