Date: Dec 30, 2012 1:35 AM
Author: kirby urner
Subject: Re: A Point on Understanding

On Sat, Dec 29, 2012 at 9:55 PM, Louis Talman <> wrote:
> On Sat, 29 Dec 2012 19:52:40 -0700, kirby urner <>
> wrote:

>> ...the sphere-at-the-limit
>> concept does not apply.

> The issue isn't whether the concept applies or not.
> It's "What do you mean by 'sphere-at-the-limit'?"

I maybe should have said "perfect sphere as the limiting case" (for an
algorithm that never really gets there, because it's always in terms
of a network -- that sets up a tension).

I also left open the option of defining away "perfect spheres"
entirely if we don't care about perfect continuity i.e. nothing really
touches anything else in our preferred set of definitions. So no
"limit case" to worry about. That wouldn't be calculus though so
epsilon / delta need not apply.

> And, remember, you'll have to deal with the notion of vertex of a
> sphere---not to mention edge and face, before you convince anyone that
> you're doing anything but demonstrating that you don't have a good,
> mathematical, handle on these notions.

I see myself more in the role of a Berkeley, fostering free-wheeling /
open debate so students might better appreciate the need for
formalisms ala those of Cauchy and Weierstrass (credited for really
getting The Calculus on a secure footing).

Those with the strong grip (secure handle) will complement my
loosening with their contrastingly tight treatments.

In the meantime, lots of important concepts get introduced and we do
some proofs of:

(a) Descartes' Deficit
(b) V + F == E + 2 (the proof in Cromwell, as he presents it,
attributed to von Staudt, is a fave)
(c) V = 10 * f * f + 2 (I've done one of these -- as Coxeter
exulted, it only takes high school level math)

It's a recognized pedagogical / andragogical technique: to re-create
the confusions so as to re-live the satisfaction of having them


> --Lou Talman
> Department of Mathematical & Computer Sciences
> Metropolitan State University of Denver
> <>