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

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  • Subject: [mg66701] Re: Interval[{a,b}]-Interval[{a,b}] = 0?
  • From: Paul Abbott <paul at>
  • Date: Sat, 27 May 2006 03:52:40 -0400 (EDT)
  • Organization: The University of Western Australia
  • References: <e510r2$8eg$> <e514do$96v$> <> <e56duk$1sn$>
  • Sender: owner-wri-mathgroup at

In article <e56duk$1sn$1 at>,
 Andrzej Kozlowski <akoz at> 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  
> definitive answer provided. I am afraid this answer is also  
> 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.


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)    

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