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MathGroup Archive 2005

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Re: Re: To be or not to be...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg62055] Re: [mg62032] Re: To be or not to be...
  • From: Pratik Desai <pdesai1 at umbc.edu>
  • Date: Thu, 10 Nov 2005 02:50:38 -0500 (EST)
  • References: <dksd37$h58$1@smc.vnet.net> <200511091005.FAA19735@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

dh wrote:

>Hi Ingolf,
>the problem is not with Sequence, but with Equal and its brethren. 
>Sequence will simply insert an empty list into these functions.
>We then have:
>
>Equal[]
>Unequal[]
>SameQ[]
>UnsameQ[]
>
>the amazing fact is that all these are giving True.
>
>The closet thing one finds in the Help is:
>
>"Equal[e] gives True."
>
>and similar for the other functions.
>Here e  means an expression. To make ends meet, one has to assume that 
>"expression" in this context"  can also mean "nothing" or no arguments. 
>  
>
One the other hand an empty set in not the same as nothing, e.g. look  
at  wikepedia's explanation of empty set

 http://en.wikipedia.org/wiki/Empty_set

Or maybe I am missing something......won't be the first time :-)

>The amazing thing here is, that in general, a pattern of f[x_] does not 
>fit f[]. Why should Equal be an exception???
>
>sincerely, Daniel
>
>Ingolf Dahl wrote:
>  
>
>>To Mathgroup,
>>
>>Try the following commands in order:
>>
>>b = Sequence[]
>>
>>b == Sequence[]
>>
>>b != Sequence[]
>>
>>b === Sequence[]
>>
>>b =!= Sequence[]
>>
>>The four last lines all evaluate to "True" for me. Quite amazing!
>>
>>Best regards
>>
>>Ingolf Dahl
>>
>>Sweden
>>
>>
>>
>>    
>>
>
>  
>


-- 
Pratik Desai
Graduate Student
UMBC
Department of Mechanical Engineering
Phone: 410 455 8134



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