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Re: Question on Positive[x]=True

• To: mathgroup at smc.vnet.net
• Subject: [mg7827] Re: [mg7791] Question on Positive[x]=True
• From: seanross at worldnet.att.net
• Date: Mon, 14 Jul 1997 03:01:10 -0400
• Sender: owner-wri-mathgroup at wolfram.com

Raya Firsov-Khanin wrote:
> 
> Dear Steve,
> 
> I have the following question.  I want to state that a variable
> x is positive. On page 1170 of the Third edition of The Mathematica book
> it is said that I can do it by making a definition
> 
>     Positive[x] = True
> 
> However, while trying to do it I get a message :
> 
> Set::write: Tag Positive in Positive[x] is Protected
> 
> Any suggestions on how one can make variables positive, negative etc?
> 
> Thanks a lot.
>                   Raya Khanin.
>                   University of Edinburgh

Protected is an attribute which must be removed before modifying.

Try 

Unprotect[Positive];
Positive[x]=True;
Protect[Positive];