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MathGroup Archive 2006

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Re: Why does Reduce work this way ...?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg67238] Re: [mg67225] Why does Reduce work this way ...?
  • From: "Carl K. Woll" <carlw at wolfram.com>
  • Date: Wed, 14 Jun 2006 06:28:44 -0400 (EDT)
  • References: <200606130507.BAA23801@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

jackgoldberg at comcast.net wrote:
> Hi folks,
> 
> This post is related to a previous series of posts about ReplaceAll in a set of inequalities.
> I have "reduced" the problem to this unexpected situation:
> 
> In[1]  FullForm[-3<=x<=1]
> Out[1]  LessEqual[-3,x,1]
> 
> In[2] Reduce[-3<=x<=1]
> Out[2]  -3<=x<=1
> 
> In[3]  FullForm[%2]
> Out[3]  Inequality[-3, LessEqual, y, LessEqual, 1]
> 
> In[4] Reduce[ LessEqual[-3,x,1]
> Out[4] -3 &#8804; x &#8804; 1
> 
> In[5] FullForm[%4]
> Out[5]  Inequality[-3, LessEqual, y, LessEqual, 1]
> 
> This defies my understanding.  What is qoing on with Reduce?
> 
> Jack

Jack,

I think that Reduce converts inequalities to a canonical form for 
further processing. The form of the inequality with head Inequality is 
more general than the one with the head LessEqual. For example,

-3<x<=1

cannot be expressed using LessEqual (or Less).

Carl Woll
Wolfram Research


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