Re: Interval[{a,b}]-Interval[{a,b}] = 0?

• To: mathgroup at smc.vnet.net
• Subject: [mg66701] Re: Interval[{a,b}]-Interval[{a,b}] = 0?
• From: Paul Abbott <paul at physics.uwa.edu.au>
• Date: Sat, 27 May 2006 03:52:40 -0400 (EDT)
• Organization: The University of Western Australia
• References: <e510r2\$8eg\$1@smc.vnet.net> <e514do\$96v\$1@smc.vnet.net> <200605250658.CAA03721@smc.vnet.net> <e56duk\$1sn\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```In article <e56duk\$1sn\$1 at smc.vnet.net>,
Andrzej Kozlowski <akoz at mimuw.edu.pl> wrote:

> Note that in Mathematica you will get things like:
>
> In[8]:=
> "a dog" - "a dog"
>
> Out[8]=
> 0
>
> Now, one could also argue that this is a bug, since first of all
> subtraction of strings (or animals) is not defined and besides there
> is no reason to assume that the second dog is the same as the first
> one. Unfortunately Mathematica is very simple minded and when it has
> no rules for dealing with some object you can always subtract it from
> itself and get 0 so this fact alone gives you potentially an infinite
> number of bugs to could complain about!
> In addition, in Lewis Carroll's "Through The Looking Glass"  the
> question of subtracting a bone from a dog is discussed and a
> unimplemented in Mathematica, so from this point of view there is
> another bug, which might  result in seriously wrong answers  in
> computations involving dogs and bones.

I would argue that there has never been a better posting on MathGroup!
Keep up the good work Andrzej. But this made me think of the line "give
her dog a bone" in "Cool for Cats" by UK Squeeze -- probably
inappropriate for this newsgroup.

Cheers,
Paul

_______________________________________________________________________
Paul Abbott                                      Phone:  61 8 6488 2734
School of Physics, M013                            Fax: +61 8 6488 1014
The University of Western Australia         (CRICOS Provider No 00126G)
AUSTRALIA                               http://physics.uwa.edu.au/~paul

```

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