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

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  • Subject: [mg66637] Re: Interval[{a,b}]-Interval[{a,b}] = 0?
  • From: "Richard Fateman" <fateman at>
  • Date: Thu, 25 May 2006 02:58:01 -0400 (EDT)
  • References: <e510r2$8eg$> <e514do$96v$>
  • Sender: owner-wri-mathgroup at

I'm sorry I was not clear in my original note, since several people
seem to think I was objecting to  [-1,1] - [-1,1] simplifying to [-2,2].
This is universally agreed to be correct in the "reliable computing"
community, for the reason given by Johan, and I certainly
agree with it.

What is likely to be a bug, in my view, is the treatment of
Interval[{a,b}]-Interval[{a,b}] , and I was just wondering if
anyone could defend  simplifying it to 0 as a feature.

The closest I got was a suggestion that  "this is not the right tool".

One correct answer might be to leave it alone.   or maybe
after ascertaining that   a,b are real and a<=b , the interval [-2*a,2*b].

The answer 0 not only is wrong, but apparently leads to bugs
in Limit computations, where Interval notation is used /abused.

"Johan Grönqvist" <johan.gronqvist at> wrote in message 
news:e514do$96v$1 at

.... snipped...   explanation of [-1,1]-[-1,1]=[-2,2] 

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