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MathGroup Archive 2005

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

  • To: mathgroup at
  • Subject: [mg62055] Re: [mg62032] Re: To be or not to be...
  • From: Pratik Desai <pdesai1 at>
  • Date: Thu, 10 Nov 2005 02:50:38 -0500 (EST)
  • References: <dksd37$h58$> <>
  • Sender: owner-wri-mathgroup at

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:
>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

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

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

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